Jelqing and squeezes will help, but a few months of pumping gave me more vascularity than a year of manual-only techniques.
The best excersize I found for veins is one I called the power jelqel squeeze. It consists of getting a full erection, doing a hard kegel then Using the power-jelq device to clamp down. Hold for a few seconds and you should see the veins get much larger. Doing this 25 times a day will do wonders.
Jelqing and squeezing will naturally give you more vascularity as a by-product of PE, and you probably won’t have much of a choice about it.
Go easy on this, veins are a easy place to incur injury. Start slow and easy.