I have made a few guys cum without touching, and I think most of the time it was when the bottom was on their stomach with my drilling from above.
The key to really hitting a bottoms pleasure centers in that position is to move your cock above his hole a bit (up north a few inches) so that when you push it in his ass there is some pressure on the top of your cock and it forces your cock downward and right into his prostate. Fuck him like that and even if he doesn't cum your bottom will be extremely appreciative.
But really the times guys have cum without touching themselves I think it had more to do with the bottom than me. I think some bottoms are just so super sensitive in their ass, something I am very jealous of, because being fucked is nice for me, but is never like the ecstasy I see bottoms experience.