- Quickly send a payment from any private key
This isn't what you wanted to do but perhaps if you want a quick and dirty solution, you can use Blockchain.info to sweep the funds from a private key to an address in your local wallet. That way you don't need to import that private key into the bitcoin.org client.
That can be done using the API:
It looks like you can feed an unsigned raw transaction and a list of private keys into the new bitcoin client and it will sign and send the transaction without storing the keys in your wallet so this seems like a good solution for sending. I can use my perlfoo to create the raw transaction.
(By the way I just had to check if 4d6c9dff493fcd2da9508e01c8b13461d37e3d8b6df1732942d3257874051362 had any money in it, damn none!)