adoubletap lace the rim to a hub with a few spokes, tape the brake surface and with a razor blade held steady cut the tape whilst turning wheel in a frame?
Sounds like it could work if you are handy with a blade !
I recommend a Swan Morton scalpel blade (a '10A' is a good shape for this kind of thing) instead of a razor blade.
Or . . .
Get two junk/cheap/old rims and sandwich the good rim between them with a pair of clamps - powdercoat - bake = remove clamps !
Sounds like it could work if you are handy with a blade !
I recommend a Swan Morton scalpel blade (a '10A' is a good shape for this kind of thing) instead of a razor blade.
Or . . .
Get two junk/cheap/old rims and sandwich the good rim between them with a pair of clamps - powdercoat - bake = remove clamps !
Hey presto un-powdercoated braking surfaces !