I feel a little bad posting this, since it's not a 100% answer, but a direction to look in....
I have a smiliar desire, and have looked into it, just not done it (so i can't guarantee it works).
first, use xev to make sure your multimedia keys are being recognized (events will show up). WIth xev you can also get the keycode for that key
Once you have those int values, you can use xmodmap to map that key to any action.
Similar things can be done with mouse buttons, i think