is this on the testnet? Or a private net?
I can possibly think of a way if it's the testnet (or mainnet, never tested, just a theory), but if it's private not a clue.
My idea is just to go to a site like blockexplorer, grab the raw transaction, edit it, resign it, rebroadcast it.
It is a private-ish (I have the majority of the hashpower on it actually.) net, but the coin is a fork of BTC. I can set up a block explorer. This seems like it should work actually. I won't be able to do it tonight, but tomorrow I can probably set up the block explorer and try this. Thanks. If it works, I will pm you for a BTC/LTC address.