jwheeler, You must have a "FICHT" Polaris Frontier, huh? Those are the only engines I'm familiar with indexing the plugs for. I don't think you will be able document any advantage with any engines that don't have direct fuel injection.
If you do want to index, just put a mark on the ceramic insulator that corresponds to the plug gap. Try various plugs until you find the ones that face the gap the way you want it. You can also vary the torque a bit to get the gap direction you want as long as you don't get carried away.
Personally, I think you will find it to be a waste of time. I don't even do it on my FICHT outboard.