I don't have an answer for ya darlin. YOu've done a lot of the more common stuff. And CBT is highly varied amongst those who enjoy it.
You might want to try adding in a chastity device for part of the time, to make their cock off limits and only the balls get your 'attention'.
Depending on your partner you could try urethral sounds, or look into using ginger/peppermint oil and applying it. I'd stay away from icyhot or any petroleum based products though. And speaking of ginger... you can always add a nice piece of it to their bottom when you are playing them. They'll quickly find out that bearing down on it causes more pain. And I'm sure you know a few ways to keep their sphincters tightly shut. lol!