Let me preface this by saying that I have never done this myself, but I have read here on the board (possibly by Rob Macks) that you can use a wet sponge to apply water directly to the bare wood on the inside of the hull. As the wood absorbes the water, the wood should swell, and the hull should move back pretty close to its original shape. Obviously you don't want to put so much water on that the glue starts to dissolve. So take it slow. But it's worth a try before you go the drastic route of sanding off all the glass on the outside and re-fairing the boat.

I'm not sure how to search for the post(s) in the archives, but maybe keywords like "sponge" "hull" "water" and "swell" might get you there.

Good luck.