If you have enough handlebar length simply loosen the shifter where it clamps to the bars and slide it inboard. On all but the shortest handlebars there's usually enough room to mount both throttle and shifter.
In addition, you'll probably find that the shifter becomes redundant. Once you get things running right, the only time you'll pedal is starting the engine. From there, the pedals are just for a place to put your feet so shifting becomes unessessary.
Good luck. Let us know how you make out.
Tom