What you are asking here presumes that what you see (the outside of the waistband) is positioned such that the inner side of the waistband connects to the skin. Unless in some way the material that fills the waistband is defined, that is not possible. There is no way you can expect a program to dream this up by itself. Solution for this has been in the cloth room since the beginning with Poser 5. Shrink the waistband until it connects to the skin and make it constrained (or cheorographed if the garment is a conformer).