Jay:
If you
still intend on trying to infill the voids, maybe you could try using colored sealing wax.... the same stuff that you use to make
intaglio impressions. It would give you a few seconds of soft time to shape and
flatten the blob in each void .... and the process is reversible if you don't like the result... just apply heat. Silver is one of the
standard colors available. It dries a dull silver gray though, rather than bright, so it will contrast with the silver of the coin. In our
area, it's sold in candle form at Michaels Arts & Crafts stores, and I think I've seen them at Curry's art supply stores as well.
Gary