Rob, I've been staring at a bike and thinking about this. Don't you think having a shift lever hanging down between the two pegs might kinda get in the way and causing constant bruising of the ankles and lower shin?

It may be doable with some sort of fixture containing a specially angled shift lever bolted behind the rider peg. Then a linkage rod could be fabricated and hooked into the primary shift lever. I see why rear-sets cost so much now, never really put much thought into them before...
I plan on making a version of this shifter without the "heel" portion so would probably use something like that with a modified angle between the toe portion and where the selector rod attaches.