Very interesting! Is there a photo of the lever set-up that you could share? I'm not visualizing how you would get it to hold focus. I have used a custom extended flexible shaft with a Beseler 45MCRX, but it did not work well at all, perhaps because the Beseler focus knob and rack are so coarse to begin with. Besides the rope trick, I can imagine removing the stock knob and fitting a chain sprocket of some sort, then hanging a loop of chain down to where a user could reach it.
I continue to appreciate the thoughtful and helpful replies!