I am genuinely curious how that would work. Can you elucidate on how it feels to have a body part that you do not actually have?
I seem to remember that when I was very young I had night-terrors in which I seemed to have two penises. But it's too distant a memory to explain it even to myself.
The point is that it's entirely possible to discuss things that are really experienced but don't really exist, without committing to any philosophy of it. If that can be accepted, then real concerns, such as locker rooms or prisons, can remain sex-based without a contradiction.