Sail versions do in fact have a clamp on the throttle control part number, 0394522. I believe this clamp could be fitted to other models.It is part #43A in the the mid section parts diagram in the parts catalog
It would entail removing the twist grip and kill switch/idle speed control, fitting part this in place of the existing friction control #43, then refitting the other components.
Often thought about doing it on my 6 hp but never got round to it. Cost of part around $20 to $25 .(I stiffened up one o fthe linkages with a fibre spacer instead)