Reassign Trackpad Gestures? The current behavior for an upward four-finger swipe on the trackpad is to move all Windows to the side and display your desktop.  I personally have no use for this since I keep absolutely nothing on my desktop.   Is there a way to reassign this gesture to something else?  

For instance, I'd like to reassign it to Activate Spaces, since I'm a heavy Spaces user.

I'd prefer a non-third party solution to this, if such a solution exists within the bowels of OSX somewhere.  If not, a third-party solution will suffice.
Possible a duplicate, but of course BetterTouchTool