I read an online article a few days back about a guy who converts Bulgarian 8x56R Berdan cases to 8x50 boxer. He rigged a jig up to drill the flash hole and remove the anvil. He then soft-soldered a piece of .22 cal shell into the pocket to reduce the pocket diameter and swaged the pockets to standard LR pocket size.
Apparently it works very well, but I imagine it's a tedious process.