I think it needs a complete disassembly to see how you could better fit a steel tension bar from beam to beam, at the front. A come-along (ratcheting cable tie-down) will pull it back to its original shape, and a well-planned steel bar or rod attached to the beams, not the trim, will keep it there. The steel can be amazingly thin and low-profile. It is better if the brackets actually wrapped over the outside surface of the beams (the top edge of the beam, which is where the outward thrust is being delivered by the rafters), so the bolts would not be under constant withdrawal stresses. 3/8" rod welded to two of the heaviest L brackets you can find would be ideal.
Casey