Yep. I think you need a modeling app like Zbrush. Pricey(600$) but flesh gets abstract at that weght. In Zbrush you can just pull things.I've done a few 300 pound figures with V3.

I don't know of any accurate body morphs out there. Then, I don't know how accurate you want to be... perhaps just sculpting a posed object is the best result. Texture stretch will be a problem, too. Fun challenge though.