Having always been sexually active, most of my skill have been devoted to controlling my orgasms, not cumming, with my mind. However, I have cum hands free a few times. After university, I did a bunch of nude modeling, both solo and with a partner, for artists who gave private classes in their studios. At one point I was asked if I would do sexual poses, erect, masturbating, being sexual with a partner. We bargained for extra fees and agreed that it might be fun. It actually was quit a challenge. Three or four times when I was posing erect for a couple of hours, using my mind to maintain my erection, and keeping my foreskin retracted, I found myself on the edge of ejaculating, and pushed it with my lower ab. muscles and kegels. I just came for the classes. They loved it by the way.
One other time I did it was watching a sex show in Sydney. The couple was amazingly hot and fucked beautifully and I got very hard... then the guy came on the girl's breasts in a shower of sperm.... and I came in my pants too.