Miners can't be repurposed to do anything except sha256d hash. It can't even do just the normal sha256, it must do two rounds of it.
It could possibly be repurposed to crack sha256d hashes, but there aren't many things (besides bitcoin) that use it.
Well... like I said there is a SHA-256 hash with a hint just waiting to be cracked, so this would be perfect if I could get it humming along.
Can I force-feed it the hash and make it think it's a network block?