Conspire with a another woman in another city to tease him with you.
When he travels to that city, make sure he's in chastity with a plastic lock. Then have him meet with that what woman (maybe a girlfriend of yours, a friend of his) and either get her to extract his chastity secret or to tip-toe around some sort of secret she's discovered about him. Then get her to give him a sealed envelope to be given exclusively to you.... which should read: “I’ve figured out that he’s a sissy, confronted him, and he says your keep him in Chastity. I think it’s cute that you do. He told me you have numbered locks for him, so if you want me to check up on him when he’s around, I’m happy to do so, just text me with the number…..boy, he’ll be very surprised....although I always knew he was a bit of a sissy."
You can share the note with him later, so he suffers some very sweet humiliation, then let him know that you’ll be taking her up on the offer!