Hmmm.... Maybe he was a (very) lateral thinker.
I suppose you could add a twist grip to the LH side of the bars, and connect it to the two outside carbys, and have the central carby connected to the RH throttle.
So "Normal Mode"; use the RH throttle, "Sports Mode"; use the LH throttle, and "The Girlfriend Wants To See Me Mode": use both!!
Richard