lol, it was just a quick thought. That's not something I can just whip up - it would take some testing and tweaking. On second thought, I'd probably use the RPM sensor hooked to a 555 timer (oscillator) in monostable mode and play with the cap and resistor values to see if I could get a the proper output signal the ESC wants to see. I built a servo tester a while back, and this would be somewhat the same, except use the rpms of the rear end as the control instead of my fingers turning a pot.
Even then, I think you'd have issues trying to match up the power levels. The power starts out small and increases with rpm in a gas engine, while BL is the opposite. It would be kinda weird to have understeer at low speed (high front-end pull from the BL) and some oversteer at high speeds (more HP from the gas engine) - kinda backwards from the norm.
Honestly, I would think it would be easier to devise a
mechanical link between the front and rear instead of rigging something like this. Would be interesting though.