It's tough. Yao's body fat is very low already. Lose weight for Yao means lose muscle and strength. He might stay on the court longer that way, but his effectiveness will suffer since he won't be much faster or mobile anyway. Instead of dominating Howard, he might get dominated by Howard if Yao loses his strength.
So the rule is to never draft a player over 7'1"(Shaq's height), because they will have stress fractures every year?
Yao might be more prone, but I never heard about George Muresan getting stress fractures and he played a git bit of years. Also, Zydrunas Ilgauskas with the Cavs was getting stress fractures in his feet every year and got it taken care of with some special orthotics and screws to stabilize the bone. It can be taken care of.