Thanks you all for your suggestions.  After thinking about it for a few days the answer came to me and it is remarkable simple.

The boxing trunks are designed to adjust to changes in the model it is near, so rather than following my normal process of shaping the model, then adding clothing, I add the boxing trunks first (no need to conform), then adjust V4's physique to my liking.  

Voila!!
The trunks adjust as I change the model, maintaining their shape relative to V4's . Once I get V4's figure the way I like the trunks fit perfectly, regardless of how curvy I make V4's waist and hips.
Whoo-hooo!