Magic Mouse: Turn it into a touchpad
Solution 1:
BetterTouchTool adds many new, fully customizable gestures to Magic Mouse and Macbook Touchpad
Solution 2:
This is answer is a bit late, but in case you never found it:
Mouse Wizard works wonderfully well and has a mode that does exactly what you're looking for. You turn the mouse sideways and use it as a normal trackpad. I actually combine that with another program, so that I can use it as a trackpad and retain two-finger-scroll capabilities.