Try this too for male subs:
https://www.amazon.com/Master-Chrome-Cock-Ring-Intruder/dp/B00U0HKC56
It's a metal anal hook with a ball attached to a cock ring. It'll stay on by itself with the ball pressing into the prostate. When the ring is on and the ball pops into place, I'm rock hard in seconds.
Bind your subs arms behind his back, and put a leash on the top of the cock ring, and your sub will follow you anywhere and beg for more tugs on the leash. Gag him maybe so he can't beg.
Now insert a regular anal hook from the back. There's enough room, and it produces a nice anal speculum effect. Put a collar on your sub with a ring at the back of his neck, and run an adjustable leather strap (or rope) between the collar ring and the anal hook ring. Cinch up the strap or rope to get the desired arch in the spine and outward thrust of the chest.
An easy improvement is to connect the leash to a harness between the top of the cock ring and a front ring on the sub's collar. Pulling the top of cock ring outward and upward at a 45 degree angle provides optimal prostate stimulation. You could also hook up the harness for the leash to nipple clamps. A little pull on the leash now will really get that chest out more.
Now you can lead your sub around in a way he won't forget. You can probably make him cum by just tugging on the leash to take him for a short walk, which would be more fun if you blindfolded him first. You'll probably want to make him stand motionless at attention for a while before you walk him around. That'll be very hard for the sub with this much stimulation. When he squirms to please himself, which I know I couldn't help doing, you'll need to punish him by whipping his cute butt.
Now I'm getting ideas for the double-hook female version.