What I'm hoping to achieve is for me to be able to hold middle-click on a mouse then perform an action by left-clicking or right-clicking.
Middle-Click + Left-Click -> Action
Middle-Click + Right-Click -> Action
So Middle-Click would be a modifier key in this scenario.
This could be broadened to include all buttons on the mouse (and keyboard?) as modifiers, as the current range of modifiers is pretty limited.
I would like to see any mouse button as modifier. I would like to replicate mouse gestures with this, such as hold right mouse, click left: send cmd-left (back) or hold right mouse, scroll wheel: send cmd-(shift)-tab.
I just paid for a license thinking this was supported, because it seemed like a basic enough feature (oops). So anyway, +1 from me..
I've only a few days left in my trial. This is the main feature I use BetterTouchTool for (currently dealing with a slightly annoying Windows Key+Left/Right click to change desktop on Mac) so it will probably decide whether I purchase or uninstall.