After seeing the excellent work done here - http://athan.se/diy-shoulder-rig/
I (obviously) thought that inexpensive plastic gears with a gear ring would make it a litle more 'proper' (or even lego gears), but the major problem was still the twist of the wrist while holding a shoulder mounted camera, which is not ideal.
No matter which way your hands are position with bars that are more horizontal, or vertical, the concept has the same problem (though its a very excellent solution for a mobile camera and pulling your own focus).
It suddenly hit me - a trigger.
You could use a trigger (like a gun), instead of any twisting motion.
The trigger pulls a spring when you press it in, which draws a line/cord/etc hooked up to pulley or other device, that converts that motion into rotating motion so you can run a gear, which then you gear up to the lens.
So as you press the trigger in, the focus moves closer (or further away), and as you let go, the spring pulls it back in the opposite direction.
I'll have to find time to start building all this shit.