Add thickness to clothes after exporting from MD without adding unnecessary geometry?

So I do have another question and it's probably Really noob, but I'm going to ask it anyway. T-Pose shoulders are a bit hard to work with in MD re: getting folds and stuff to fall right. So I tried setting up more of an A pose (I think?) sort of like the default MD avis, but of course when I rigged it the garment popped right back into T-Pose. (lol) But, when I upload to SL there's always an issue with shoulder straps bleeding into the body no matter how I rig them. Is it just best to leave the arms where they are and maybe add more detail with ZBrush, and maybe make garments a little larger around the shoulder area? I finally made some pants and encountered the dreaded sticky pants (!!!!) If there's a reason not to rig in a relaxed pose I will totally take your word for it.