Unfortunately no, I'm a bit of a 3D noob to be honest. I've used the "render to texture" to put light or shadows onto a texture before, but didn't even realise it could be used for anything else
I was kind of thinking if it was possible to rearrange the UV map, so it was head in top left, body in bottom left, legs in bottom right etc, it would be far easier to use or adapt all existing textures to the other models.
I quickly knocked together an
example - which is obviously a bit messy (most of it is very misplaced and badly aligned), but it's halfway there just by moving the UVs around the sheet in 2 minutes, without redoing the whole thing. If the body, shoes, groin and hands were remapped, and the legs and arms were resized slightly, it should work perfectly.
Obviously redoing the UVs would be quite a lot of extra work now, but would save a lot of work later on - so you'd instantly have a full set of underclothes from the existing textures, so after resizing the existing armours (like we do already for female / male), you'd have a full set of armours available for each body type, and adding new ones would equally be as easy.
I'm sure some of them would need some slight redrawing, and the ghoul / supermutant would need quite a lot of retexturing, but this could be done by editing the existing textures, rather than fully producing many textures for each set of clothes - and we obviously don't want the situation where they all end up half finished, so you have "fat man can't wear a leather jacket".
I'd happily volunteer to attempt remapping these if needed (after I've finished the models I'm working on now) - of course, if anyone has a clever way of making this even easier, then completely ignore everything I said