I didn't quite follow your previous post about push buttons and relays, but a thought occurred, what would happen if you continued to hold the throttle on the electric system at WOT while the gas system accelerated beyond the 15 MPH max of the electric system?
Of course you are risking frying something in the controller, since, for one thing that hub motor will soon be producing more than 24 volts, and of course as many amps as it can to the battery, if that's what happens. I do remember that when using my BD36 on my old recumbent bike and pedaling along, such as just after cresting a hill, there would be a point where the bike would be easier to pedal when I released the throttle. i.e., I had reached the speed where the motor was working as a generator and (probably) charging the battery, hence creating a little braking resistance. Not very scientific test, and if I said something wrong I don't take credit for it.
Reedsport? Went to school in Waldport (few years ago, I'm 75 now), Lived in Port Orford since retirement, until 2 years ago. Friend with the handcycle lives at Myrtle Point and I try to get down there a couple of times every year to ride with him.