In MCPPrefs switch to Hotkeys tab, select Active Window under MousePointer, press the Definition button, adjust the Mouse entry to eg. DoubleClick, press the upper Sample button and click once with your left mouse button. This way you tell the program to use the left mouse button for this operation.
Do the same with Active Window to Front entry in Hotkeys tab.
Now save the settings and reboot. From now on you should be able to bring windows to front with a left mouse doubleclick.
This way it can be assigned even to a single click of middle mouse button or whatever.