Override iTunes "media" keys (play, pause, etc) for Spotify?

Is it possible to set Spotify as the default program when the "media" keys (play, pause, previous, next, etc) are pressed on the Mac keyboard? For the most part when Spotify is open, the "media" keys work fine. But every once and a while iTunes will pop up when you hit them. It'd be a lot nicer if you could just specify that Spotify is the default program when these keys are triggered, as oppose to iTunes. If it matters, I'm using Mountain Lion.