Making a caul is a good idea, but I've done it just with a wide shim if I wanted a more angular, less rounded bend.
Like, get a "base" board and lay a 3/4" thick pine board on that. Place the bow back down and clamp or tie to both boards, with the lever hanging out over the end of the second board. Then, heat the transition area and base of the lever, pulling the tip of the lever with a weight or slowly tightening a cord to bring the tip down.
Good luck.