Would someone please write a quick apple script or other snippet that can reside somewhere (on my desktop, or the icon menu in the top right of the Mac OS X menu, near the clock, that has a Mouse LightSwitch?, or apply to an icon in the dock)?

Turn Mouse Middle Scroll Button's "Click" to :

LightSwitch (up/on) 

Function 1: Button 3

 Function 2: Expose - All Windows.

 As a mac user, I have come to rely on Expose - All Windows to quickly get to buried windows.  Using SketchUp i s a larger portion of my day more recently, so I often have that button set to Button 3, vs., my preferred function the rest of the time.

I'd love it if there was a one-click back and
forth way to change this.

Thank you.