A metal strapping band clamped to the belly will help prevent that. Even so, I doubt you could get that much bend with dry heat without damaging the belly. It just cannot stretch that much. A more round curve would help. But, those kind of splits generally do not cause the bow to fail. Since they are in a static recurve, by definition, they will not bend. If they do, they will fail. Keep it thick and narrow and you will be fine. I generally stay at 1/2" thickness on static tips. I also make them less than 1/2" wide most of the time to reduce mass. I've built statics up to 60# with those dimensions.