I have an idea in my head, but not seeing behind the panel of a KitFox, I don't know if it would work. My thought has the three throttle's connected to some solid linkage, a pivoting bar perhaps, bearings on the ends attached to the frame. Each throttle is connected to a lobe coming off this pivoting bar. They all move in unison 100%. Then another lobe coming off the bar is the connection point for the throttle cable(s). I'm quite sure it could be made failure proof.
However, as others have pointed out, once you have the muscle memory to fly from either seat, this all become irrelevant.