I use a $1 o-ring from a hardware store. The o-ring fits between the throttle housing and edge of the rubber grip. Provides enough friction to hold the throttle but easily defeated (or removed). I use a 1.5" X 1/8" thick o-ring.
Here's a thread from TriumphRat.net that shows a photo:
O-ring Cruise Control Thread I rode to Syraucuse with mine, works like a charm.
