Even better, a story where the guy gets the girl and they enjoy each other in several different positions, only at the very end you discover the guy was actually a chick with a dick.
You would have to rely on vague and unrevealing angles which I don't think I have to tell you is impossible in hentai. Maybe she has a strap-on and it's revealed to be hollow and filled with her actual penis.
I wonder if he would enjoy some post-modern hentai issue about the creepy men who draw these ladies. Then at the end it shows 10,000 guys that look like him enjoying the comic "in several different positions."
I found and downloaded an issue of this anthology, and the one I picked had a 'story' about some fat otaku's obsession with a model and how he'd regularly beat off on her photos. Then there was some old, liverspotted cretin and then I deleted the file.
But I think the point is that he's too far gone to feel any shame except the plain ol' primeval dick fear.