I use Kaoko Throttle Lock. Works like a champ, Easy 5 minute or less to install and adjust, looks like it could have come from the factory with it.

Mfg PN HND31. It comes with two endcap plastic washers...one for bikes with heated grips, one without.

Similar products are Throttlemeister and BrakeAway. (around the same price range)

Install is a removal of your current end cap, press in the prongs holding the weight into the bar and remove, then push in the throttle lock, tighten the bolt til snug and use the small hex key to adjust the pressure. There are a number of less costly options that I've seen work with the heated grips, like Go Cruise, VistaCruise, Kuryakyn, crampbuster, Omnicruise, but not sure they were intended for use on them.