How about one of these

[Old Timer]

Come on Onmebike/NRG sort out how to wire this kiddie in

Crystalyte Electric Bike Cruise Control on eBay (end time 14-Mar-10 06:30:13 GMT)

 

[flecc]

This is intended for the high speed direct drive motors from Crystalyte, it's unlikely to be suitable for use with your SB type hub motor controller.
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[onmebike]

Come on Onmebike/NRG sort out how to wire this kiddie in

Crystalyte Electric Bike Cruise Control on eBay (end time 14-Mar-10 06:30:13 GMT)

Although not suitable for our bike's it has given me an idea for a twist grip locking device which will lock throttle in desired position until either manually released or application of either brake releases it. Watch this space?