Part of the trick to posing overweight or "fleshy" people is if just doing head or face shots is to have them sitting with their arms on, say, a table. Then have them sit up straight then leaning slightly forwards which tightens the skin around their neck.

Then you also have them lift their chins up slightly and that tightens the skin even more.

The attached picture is shooting up her nose, so as David said make sure the camera angle is higher than that.

MIchael