There is a mechanism called CPFP (child pays for parent) which is currently implemented by one pool only as far as I know (Eligius).
This mechanism allows you to send a transaction spending one of the outputs of the original transaction with a higher fee that would suffice for both transactions. A Miner implementing CPFP can get the fee from this second transaction only if it includes the first transaction, too.
However, I would not put too much hope on CPFP - I just found a reddit thread discussion this, and it looks like it's not really working:
https://www.reddit.com/r/Bitcoin/comments/3r1dad/what_pools_implement_cpfp/So apparently your only option is to wait. Eventually your transaction will be mined.
Onkel Paul