What transmitter are you using? With a Futaba 9C, you can program some rediculous dual rates/ exponential, that would probably allow this kind of motion.

FWIW - it looks to me like they didn't mark the location of one axle. I can see how this gizmo would work. If you want, I'll add my notes and repost it. I would make this out of thin aluminum, use very tight tolerances, and keep it lubed with silicone