Hmmm, that could be a toughy. Some suggestions:
Wider than the usual, rubber bands(1/8th of an inch). Cut them to length and paint them black. That will also help stiffen them up and maybe mold to shape.
Strips of leather. You can buy some scrap or get some scraps of leather and cut it basically however you want.
Or maybe even using silver masking tape. Cut the desired size for the belt and then fold it over once. Benefit to that would be that is would be a little stiffer and once painted, could look realistic.
Can't think of anything else. Hope that helps out a little.
