First. Why doesn’t this article have comments. 2nd. Would it be possible to put the clutch gear on the bottom tube, and adjusted via a spring and screw, and mount the derailleur in such a way that it’s tucked next to the bottom bracket of the rear triangle? This would allow for the setup to not be high pivot, but the only worry would be chain slap slapping an actual chain. I guess to avoid this you could make the rear triangle into 3 separate sections so both chains would have space to travel through, and helps reduce chain contact against its self.

 I don’t know how to CAD, or I would create a 3D Model to show.