You don't have to keep stroking your dick while getting your prostate pounded to cum completely, just don't let up on stimulating your prostate, and you'll get fully drained of cum. As much as it's a mind shattering sexual experience, it's also a medical fact.
A doctor will perform a prostate massage on men who have prostate problems, this causes a VERY intense ejaculation, this procedure is called "prostate milking". Of course, unless you're really attracted to your doctor, this won't be a very pleasant experience. But with the right toy, or the right partner, prostate milking is magical. Sometimes I just need a "me" day, and I'll stay home alone and just use different vibrating toys and just cum over and over. The great thing about using a powerful vibrating
dildo is that the sensations are so jarring that you can have a mind blowing orgasm without even cumming, the stimulation of the prostate alone is orgasmic. After I have an orgasm I don't take the toy out, I just leave it in and ride the vibrations until I have another orgasm. You really need to try it. It's actually so completely satisfying that you won't even mind not having a man fucking you. Once you get the hang of it, cumming hands free is easy. Any guy who fucks you will love that he made you cum like a maniac hands free! When my boyfriend sees my cum blasting out just from him slamming my prostate, he ends up cumming too. Sometimes we both will use our toys on ourselves side by side and ride the waves together.
There is also a health benefit to prostate stimulation: it greatly reduces the chances of you getting prostate cancer.