I have this guitar in for repair. The Oasis humidifier let go inside the instrument, and the puddle sat on the inside of the back. The back seam is puckered and distorted out( the back strips had curled away, and I've removed the loose ones). I've been wetting and clamping the areas between the braces, attempting to reflatten the seam. So far, not much success. I think I may need to heat the area from the inside(enough to make it pliable, but not enough to damage the finish)before clamping. Anyone dealt with this situation before? These Oasis humidifiers seem to be little time bombs!
I had a Martin OM28V in for repair, the guitar had been left too close to the heater for one night. The back strips were loose, the inlay was damaged, the braces were loose, the back wasn't warped so much though. I removed what's left of the inlay strip and the back strips inside, which alowed me to reflatten the the seam and to reglue it to the braces. New inlay, back strips glued back, back refinished. It's a major and costly repair case but I think you need to remove the inlay strip to give the halves of the back freedom to be reflatten, it's easier to correct the gap width for the inlay, than to force 2 glue joints, 2 warped rosewood pieces and the multi layer inlay strip back into their place, all 3 swollen from watering. Martin sell inlay strips in their 1833 Shop for $6 (2 pieces).
Ah, clamping! Another benefit of removing the inlay strip is that you can use some bolt & nut clamping system to gradually put the back halves into place. Otherwise, you can try really strong magnets (worked for me a few times) though I can't say how much resistance there is in the warped rosewood there. If the "curb" is really stiff any clamping won't help much without additional measures (I used small silicon heating blankets in one of the cases like thatt) and I'm not sure the finish can be saved then :(
How about loosening the braces, laying the guitar on its back on a flat, stiff table, and using bar clamps on the sides to force the center flat? Then reglue braces using jacks.