PondsForFun,
I really think the Tilapia are the key, without them, you don't stand a chance, with them, maybe...that's just my opinion.
If you were willing to drive to Livingston, I believe I could get you some flatheads from the Trinity river. I assume that is legal. However, I've never seen one smaller than around 5-10 pounds. They must exist and if you are interested, I know some guys who can find them.