Take it to Apple and pay to place some more RAM into the machine.
Lets see, Apple quoted me $435 to upgrade to 8GB, so since you likely need 4GB I'd say they would likely charge about $380.
You could add more RAM yourself, there is a little door under there someplace, there is Crucial.com which will give you the right RAM for your machine, there are videos on YouTube, so I guess you could add more RAM yourself to save a lot of money.