i have just bought a thumb throttle to add to my wife's Hopper Shopper SE.. This one , http://www.banggood.com/78in-Universal-Thumb-Throttle-Speed-Control-E-Bike-Electric-Bike-Scooter-3-Wires-p-982047.html..
I followed the advice on here, removed the cover and found the spare 3 pin connector...