The penis is good for a bit of torture. This is like the mans pleasure centre, or pain centre, depending on which way you look at it. So where do you start with all this cock and ball torture. Maybe a little twist, or a grab of the testicles. Again, gently is the order of the day.
If you fancy it a bit harder, a slap of the cock with a hand is always a good start. Dont start smacking the balls though because they are delicate! Doesn't mean they cant be squeezed or pinched.
Want it even pervier, you can delicatly (delicatly) use a leather tawse to introduce a sting into the cock. Again, it's all a highly charged sexual atmosphere. Men tied down and strapped up and begging to be teased and tortured by a superior female till she squeels with laughter at an inferior males pain.
Just remember, be careful!