Program to assign mouse button chords? Is there an app to assign actions (such as shortcut keys) to mouse button chords?

For example, button 1 + button 4 = Cmd+C, button 4 alone = Cmd+V, etc.

I have tried a few utilities, but none of them support assigning a custom action to two buttons pressed at the same time.
Better Touch Tool can do what you want, and can even be set up to do so on a per-app basis.