Their UVs are shared, so if you create two layers in SPP, one with the male textures and one with the female textures, you can use a mask to fill in the crotch on the male texture.
I should put up the spp file for the SFW male though
I would try to do the two layer method but unfortunately I'm not the brightest so I don't really know how to do what you're suggesting, I'll likely just wait for the SFW files instead since, knowing me, it'll be easier that way tbh
