How Do I Ask?
Spice things up a bit, take charge and play the dome role,I'm a man and my biggest fantasy is fir my wife to take this role and to bring it with pegging, the switch thing is amazing, it's sex our of the constants of your normal rut.... just try different things. Going a little further each time, at some point touch his arse, he will love it I promise, go slow, once you ever touch his hole or slip a tongue in him he is yours, try tying him up, work his nipples, after he's really turned on, lube a finger and ease it in him, work his prostate ,he will totally submit... once he comes from anal play there's no going back, even better if you are training him to submit, spank him, then start fucking him, once a man ever takes it he's your to use...
Just ask!
I'd love it since I'm already into the kink. If he's remotely into it he'll accept.
Now how to ask? Just be yourself... he knows you, you know him, just try what you think works best to get to a point where he's ready to listen to your desire.
Just ask! The wife and I started doing it a year or so ago (I asked) and we love it. Recently bought a strapless strapon with a prostate massager, when she put it in I instantly had a prostate orgasms. Last weekend she had an orgasm while she was doing me.