hum.... maybe you could make a customized support for your engine that can move right/left and put a conic spindle. with a vertical handlebar to move it, and holes on horiz. rack (0,5 inch between each) to hold it in place, it would be like shifting a CVT... do you understand? (because i'm french, so it may not be very clear...)


EDIT: I made this picture to show the mechanism... the whole rack moves left/right and stops on a horizontal rack soldered on the bike frame...