[SOLVED] Shirt texture goes over bottom's.

How can I "prioritise" textures? I'm making a t-shirt and it's supposed to go tucked in. It's semi transparent and skin-tight so I can't really change the UV map; I used the male nude top mesh as a base. The problem is that the shirt's texture goes over the bottom's texture and it should go under it; I made the texture a bit longer in case someone wanted to use the shirt with some low waist pants, but I guess it kinda backfired.

Thanks for reading.

This is what it looks like in S4S.