Have him lay on his back with his head over the edge of the bed, put the strap-on in his mouth and make him take it down his throat. He’s going to gag. Alot. It’s going to take many attempts but eventually he will be able to let you throat fuck him. There’s nothing like watching your man taking a long slim dildo all the way down his throat for you.
When pegging him make him cum on your fingers, then with the dildo still in him, lift your fingers to his mouth. He will be reluctant the first few times. A couple of sharp thrusts will usually make him open his mouth at which point you can cup your fingers over his mouth to force him to do it.