This is more debilitating than a humbler

Hang onto the keys for your friend's sub.  Benefits: - It teaches him to be very nice to her friends.  She can let him know who has it, or just leave that open.  It is fun, though to show it off to him, so he knows, and stays submissive - you can help encourage him to remain submissive if he ever wants moments of release - It makes it easier for her to keep him in chastity despite how much he might BEG or whine - It intensifies the risk as a couple, which heightens the teasing even more - she will be grateful to you and willing to try new challenges with you. - what an extra tease for your husband, knowing [...]

Let him see her doing things to you that he wants her to do to him.  This pushes his boundary of submissiveness to new heights.

Tying him up, and teasing his wife is amazing. He seems to want to be jealous, but doesn't want it end.  Especially if you leave him uncaged during the teasing!

He has two holes.  When working with a friend, make use of both of them.  More efficient use of time, and twice the humiliation

He needs to learn and know that he can be pegged by whomever you chose.  He is yours to control.

Once you have been educated on the benefits and value of femdom, pass it on.

Ruin his orgasm while pegging him.  He will want more