Mr W refuses, and I respect that, but i think he'd like it if we tried ???
Firstly, if I understand you correctly (by your handle) you are submissive to Mr. W. So one wonders if he considers this interest of yours "topping from bottom" or trying to go beyond his limits.

If you are switching with him and you wish to top him through the use of anal play and he agrees totally to submit (and doesn't negotiate this out as a hard limit), I'd recommend that you go slowly, as lots can get hurt up there.

Fingernails are out. Trim the nail of any finger that is going to penetrate. Large toys (at first) are out. Go with the "fisting" model in which the person being fisted gets control so that the person inserting said fist takes cues from the person being fisted and does not penetrate too swiftly, suddenly or beyond the capacity of the person being fisted. Any tear in that area could result in a really bad trip to the hospital. Also make sure that anything inserted may be fairly easily pulled out (which means the thing inserted has to have something that extends outside of the rectum).

I have taken quite a number of strapons (and other devices). It's a fave with Dommes as it's a totally dominant position for them. With respect to the prostate massage, it's not a "G" spot for me. I always lost any erection I had before and I don't get it back until that which was inserted is fully removed. So the joy I receive in anal play is the joy that comes with the power exchange. I am attracted to men but not so much on a sexual level as on an intellectual level. I am not terrified of another naked penis in the room but I'm not craving to offer it a blowjob.

Any couple interested in understanding this more ought to get a copy of Bend Over Boyfriend by Carol Queen and Robert Morgan. It's a great resource, even though I have never experienced the "prostate stimulation orgasm" described in the video (though not from failing to try).