I'm wondering if there is a functional *forward* (or lateral) bias or is it all vertical when you are on the bike? If there is a lateral bias then it would be similar to having a short femur... which is my issue... same left side and same amount... 3/4" (~2cm).

The best help I got was using a 5mm forward cleat position, and 5mm shorter left crank. A spacer alone might be better for you. At any rate, you need to go through the whole pedal stroke and try to compensate for ~50% of the difference... don't try for 100%, and make sure that you don't cause some parts of the stroke to be even worse! The power phase is the most important part to get right.