There is a type of flexible foam that can be shaped as it forms. It comes in two components, that are mixed, like epoxy, and then expands during the chemical reaction. After curing, it is flexible, like the foam used on matresses and sofas. There are even colorants that can be mixed to it to give it a color different than the light brown, tan-like original. I bought a couple of cans years ago, on a shop that sells stuff for surf gear. I still have some. After mixing it, it can be poured on to a mold, and it will cure in the shape of the mold. So, if you made a mold with the shapes you want, and pour some of this stuff in to it, you would end up with a piece tah can be inserted on the limb, and then glued and painted. It is not very heavy, and it is very flexible and soft, so it wouldn't hinder the bow's function very much. Hope this helps.
DF