Maybe depends how far you want to go with it...but my initial reaction when reading the post was - moisture, heat and pressure. It would require sanding the fin and repainting. I was asleep that day in physics, but it seems to me that the fin will tend to spring back to the warped position by just clamping and releasing... Though there is probably some math to determine a perfect pressure and/or heat.
If nobody said anything to me - I would sand the paint off, mist it pretty heavy, heat and clamp....maybe repeating every day???? Right or wrong that would have been my plan.