Of course, watching you cum isn't the only thing that I like. I also get a kick out of humiliating my little wanking pet. That means it's very important that if you do start to cum, you have to carry on with whatever tricky stroking method I allowed you at the time.
No switching to easy, cheater-butt. Don't think I don't know how tempted you are to just wank it easy. Just think, if it does work, and you do get to cum not-so-easy, it could be an exciting new sensation you discover.
Anywho, go ahead and drum on your dick for a little while. Just the fingertips, drumming like rain. Drum your balls too. Pitter-patter, pitter-patter.