Hmmm, interesting. I had not heard of a whippletree before, but I recognize the mechanism. Not sure I would have the width available to accommodate the width required for the system of levers. Can you think of anything similar using pulleys?
I have a very compact device that I'm designing. It pulls cords (fishing line) that operate the chords on a guitar for people not able to use the fret board.
Here the problem - a first class lever pulls on three cords simultaneously in response to finger pressure on the other end of the lever...