If you use porn or vivid fantasy, maybe some lube or really soft stroking making your dick 100% erect. If you keep stimulating it to keep it 100%, but never kegel. Focus on relaxing and visualising it grows, I find that my erections gets extreme, like the veins are going to pop. Anyone tried doing this as a part of their PE session?
Or maybe someone already experimented and realized that the super-hard penis was due to the sensation, and this is just a normal good erection?