To be honest, I don't really understand why this isn't already possible right now - even for 3-finger and 2-finger-gestures. I'd really like to program the multi touch gestures the way I like which would also include a gesture to open the dashboard. Anyway, there a little program called "MultiClutch" (think it wasn't mentioned before) which lets you individually program the 3-finger-gestures. As I had problems to configure it the way I like (I think it was a problem for me to program the "F"-keys, if I remember correctly), I don't use it, but mabye it is useful for some folks out there ...