Idea: From the Bottom
This one is not something I’d indulge in personally since I’m not interested in being on bottom ever, but it is a hot idea all the same.
A sub, kept perpetually in a chastity cage, is fitted with a strap-on dildo. Perhaps made from a mold of his own cock. He’s then forced to fuck his dom (who tops from the bottom) when they have sex.
Only one of them gets off. Not much question which.