I've been looking for one of these for years - no success so far. The am on the twistgrip doesn't really ssem up for modification but I reckon there is scope for changing the metal plaes at the TB end - ones with smaller diameters would do the job for not much cash. Surely someone must be able to knock up such a thing and relieve all that twisty turny nonsense when you want to hit the go juice.
LC