OH gosh yes, the easiest way is to get a really strong vibe and find just the right spot on the cage or under his balls. You’ll know you’ve got it by the sounds he makes.
The other option is anal stimulation, again easiest is a butt plug or even better a prostrate massager with a strong vibe pushed on it or an actual thin prostate massager vibe. But what most really want I think is being pegged (you using a strap on dildo on them) or simply just a dildo.
Of course when he’s caged I’m always very tempted to make it a ruin, and I usually do. It just seems right to start it spurting and then just stop and watch it and giggle, plus it keeps him hornier which is the idea.
And whispering ‘why there’s no reason to let you out at all now’ always drives him crazy…
A few fun little things too, one is when he starts to ask to cum, tell him to ask to ruin it instead, make him beg for that, that’s kinda hot. The other thing is tell him you will but only if he eats it afterwards. Now the thing with that is it’s not a big turn on unless I’m super horny and feeling mean, and honestly it doesn’t matter if you do it or not, but just making him say he will before hand is a real thrill for you both, well it is for us anyway!