Here is an article that may serve as a good reference, particularly the sections on the Levitor Ani and External Sphincter: Anatomy and Neurocontrol of the Pelvic Floor . I’m pretty sure the pudendal nerve plays a big role in what goes on when we short circuit or override the instinctual impulse to ejaculate. It’s a somatic nerve that passes through all of the muscle groups of the lower pelvis and out to the tip of the penis.
I don’t think you need to completely isolate the various muscles of the pelvic floor—they are all intimately related. However, I do think it’s important to practice centering contractions in various locales and getting a feeling for the difference between "pushing" and "pulling." I think the "stirring and swirling" thing alluded to briefly in the OP can help with this, so I’ll try and expand on it a little.
It might be helpful to start off thinking in terms of three centers to focus contractions on: The prostate, the tail bone (coccyx), and the root or bulb of the penis (or the point where the perineum meets the anus.) Since hopefully everyone has been doing kegels, let’s start with isolating the root. Do these exercises flaccid to begin with—I think this way it’s easier to focus on the muscles involved and tune into the direction of force. You can do these sitting or standing. Start by doing a kegel, then continue to clench harder until you are involving your anus and all of the pelvic muscles. Now, holding the full pelvic clench, try and "pump" the area right at the bulb—contract that area harder, then "release" without releasing the overall pelvic contraction. This should activate the whole perineum and you should feel (if not see) your flaccid penis twitch a little in response. Your penis should pull up (or feel like it’s pulling up) or maybe even turtle a little when you contract the area, then relax back out when you "release." That’s the nerves responding to stimuli (let’s call the feeling of that nervous reaction "energy.") Now release completely, relax, and repeat. Once you’ve got the hang of isolating the perineal center while doing a full pelvic clench, play around with churning, pushing, and pulling the "energy." Try and do little circles, then "move" the "energy" up to the tip of the penis. With practice, you should actually be able to feel this, and it requires only very slight, subtle muscular movements of the isolated area. You’ll notice that a lot of it is in the brain—you are focusing your awareness on the area, your muscles respond to your brain’s commands/suggestions, and the nerves in turn respond.
OK, now let’s do the tail bone. Begin with an anal clench focusing on the posterior side. Try and pull your tail bone in as you slowly increase the force of the contraction to again encompass all of the pelvic floor muscles, including the BC and PC. Now, fully clenched, concentrate on the muscles surrounding your tail bone and STIR. It should really feel like you are stirring your tail bone—I mean you are actually, physically moving it around.You should be able to feel it moving if you place your hand back there. It should also feel mildly pleasant, but with the location of the pleasure centered in and around your tail bone and up your spine slightly, not in your perineum or penis. Again, clench and "release" this area as you stir while holding the overall pelvic contraction. Also, continue to move the overall contraction further up the sphincter and Levitor Ani until you feel a mildly pleasant sensation in your prostate area—if you clench this deeply, you will in fact be giving your prostate a mild internal massage by squeezing it gently. Then move the focus/nerve response/"energy" back down to the tip of the tailbone and up again while you continue to stir.
If you had a hard time feeling the prostate’s involvement in the above exercise, try doing an anal clench without isolating any particular area, then continue to strengthen the clench so it goes deeper and deeper. Your anus should be pulled up. Continue to squeeze harder and tighter, then bear down/push from above gently at the same time. Now relax and repeat. Do you feel a mildly pleasant, possibly "weird" sensation several inches up and inside as you clench and release? If so, that’s your prostate. If not, maybe some others who know what I’m talking about can try to describe isolating this area. Once you’ve isolated it, take the approach described in the above exercises and begin the pelvic clench from that area. If you have a hard time beginning there, then do the tailbone version, but once the clench is in full effect move to the prostate area and practice "pumping" it.
One further note: Practice isolating each side of the muscles involved as well, particularly the sphincters. This will help later when you get into "stirring and swirling," below…
OK, now we can begin to talk about "stirring and swirling." Basically, try doing the above exercises but without doing the overall pelvic contraction. In other words, you are relaxed, but you are moving the focus of your attention to one or another of the three centers and gently moving the "energy" around. The actual muscle contractions should be very slight—just sufficient to activate the nerves. With practice, you should be able to do this using virtually only the mind. But just let whatever happens physically happen as your body follows your mental focus, and stay as relaxed as possible (when I say "relaxed" I mean overall—obviously there will be isolated muscle movement and contractions as you do the exercises.) Now, once you’ve played around with each of the areas separately, move from one to the other. With a little practice you should start to feel that "ball of energy" thing going on. What’s really interesting to me is that it can be intensely (yet subtly) pleasurable, and there is some kind of arousal happening, but the external genitals are not involved directly at all. You’re exploring the sources and foundations of arousal, yet the penis itself is not directly involved at all. Eventually, subtle pressure starts to build up (the "ball" is "inflating" or becoming more dense, perhaps), at which point you can pull that energy up and into your body through the tail bone, or push it out to the body of the penis. If you focus on pushing the ball out, you should start to become at least slightly erect. If you have not ejaculated for several days you can even do hands free masturbation, even to the point of ejaculation if you wish. It is also possible to have internal orgasms in the same manner.
If you practice this for a few weeks, I think you’ll discover some very interesting and profound-yet-subtle things about your body, your arousal patterns, and what is possible with energy. The sensations you experience may be intensely pleasurable, yet qualitatively different from anything you’ve experienced before.
I should say also that this is something I discovered on my own during a period of celibacy that included no masturbation, so it is very possible that you have to have quite a bit of "energy" stored up to do the hands-free masturbation thing to the point I described. This might be why it’s so hard to explain—it’s very subjective, and I’ve never seen this stuff written about before. It was however a big breakthrough/discovery for me, and I do think it’s useful if not essential information, so I hope I’ve been successful in communicating it.
EDIT: A couple more points to avoid confusion: the real objective here is NOT to be able to do hands-free masturbation. I only mentioned it in passing to give a sense of how powerful and real this kind of internal stimulation/arousal can be. When I was discovering this technique and teaching it to myself many years ago, I did ejaculate a couple of times just to see if it was possible (and again, this was during a period of no standard masturbation with long periods of semen retention, so I was already at a high base level of arousal.) I also did several internal orgasms by moving the energy into the penis and getting right to the PONR before pulling it back up and in through the tailbone. More often though, I would "pull" the energy up and spread it long before the PONR, often not even focusing the energy on my penis at all. With "stirring and swirling" you can generate a high level of arousal without even allowing an erection.
The big "secret" involved here is that energy and arousal can be generated, cultivated, and moved around purely internally.
