Maybe have some situation where the protagonist is presented with the opportunity, but turns it down without the player having any input. Have him say something like "sorry, I understand the value of sodomizing our defeated foes to reinforce our dominance, but I've just never been able to get it up for men." Serves the desired worldbuilding function without compromising your vision of the character or requiring you to spend time depicting a kink you aren't into. Alternately, if you decided you did want to put it in the game, I guess you could hire a ghostwriter for that scene so it feels authentic.
I don't think the result is going to be worth the effort. An off hand mention of something happening off screen doesn't really add much to a scene, and Z is not going to hire someone to do renders for him to add something the game can do without. The budget for such a thing simply isn't there yet, and we're not short on kinks and sexual proclivities we want to add and explore without adding stuff purely to check a box and entice a specific player demographic, much like we're not going to add a scat scene purely to entice the scat fetishists into patronising the game (no parallel between lgbt and scat intented, I'm just making a point about kinks and sexual content)... Unless Z decides that he really wants to add either type of content, it's just not going to happen.
We do mention in the lore that there are gay and lesbian couples and they aren't discriminated against. We will mention this again and possibly show it from a social interaction point of view. How much of what they get up to in the bedroom we will explore on screen, is up to Z to determine.
The most that I can see happen at the moment, is that a character mentions having had male on male sex and this being a motivation for that character to take or not take an action.
Whether that would add anything to the game lore or depth wise is an open question and right now I would have to shoehorn that in a scene, because we just don't have a character or plotline that requires or justifies it...
And as I said, I'm not in favour of adding content purely to satisfy a target demographic. This, for me at least, remains a hobby.
Z might decide otherwise, and it would be a purely commercial decision, as is in his right, but when that happens, we'll see it on the screen, until then, suggestions for the sake of debate such as this are always welcome but they are most likely not going to alter the already existing trajectory of where the game is going, plot and content-wise.