Ok, I heard back from Leeds. I asked:
Is it technically possible but you don't sell this type of throttle for the 250 series or is it technically not possible?
They responded:
We don't sell that type of throttle, and if you were to use another one it would put your kit out of warranty if it isn't already.
I'm not really worried about the warranty at this point. What information is needed to figure this out? The battery is sewn up into a bag and I assume the lump towards the front is the controller. I can't see any specifics without tearing out the stitches on the battery bag.