OK... I did it, and I wouldn't recommend anyone wasting their time trying it. First I tried to put weight on the top and heat from underneath. BAD MOVE, I warped some of the ribs and had to straighten them out best I could. Three of them are beyond straightening
Then I tried to turn it over, put a narrow support in the middle and apply heat from the top. NOPE, that didn't work well either.
My conclusion is that a LOT of heat has to be applied UNIFORMLY over the entire part and pressure applied to the warp slightly beyond straight in order for it to work. My guess is that one might get slightly more favorable results by using an oven perhpas. In my opinion, buying a repro is probably the best way to go so I'm not wasting my time on any more experiments. If anyone gets a good idea and tries it I'm sure plenty of folks around here could benefit from sharing their experience.