On my old laptop, because the trackpad was close to the keyboard, it being a laptop and all -- I used SizzlingKeys to allow me to use key-combinations to control iTunes, my laptop being built prior to when they start including the media control keys on the keyboards.
Controlling iTunes using the Magic Mouse is just a matter of combining the functionality of the two applications. I tried mapping BTT gestures to the media F keys, but rather than passing the key to BTT, it just performed its preprogrammed function. Here are some screenshots that show the configuration I set up.
[crarko adds: I haven't tested this one.]

