I’m not really a two-speeder type, but can confirm that there have been two or three different ways of rigging up a hand clutch, perhaps better called a neutral finder, rather than a clutch to be used for starting off from a standstill, although I have an idea that one method did give this facility. It would take a trawl through old Yowl indices to find the articles, but I can remember that one idea came from a man called W.C.Fox, and another from the journalist ‘Wharfedale’. I think, (not too sure), that George Reeves also devised something similar. The obvious way to do it would be to connect two cables to the gear pedal boss, so as to give a pull onto the drum in either direction, perhaps operated by a double-cable twistgrip on the L/H handlebar.
I seem to remember Titch Allen being quite enthusiastic about this and he may have had it on his 2 Speeder. It was, I believe, a neutral finder rather than a hand method to engage the low speed clutch. Personally I have my 2 speed gear adjusted so that one has to keep one’s foot on the Low pedal to keep it engaged, thus it will not drive if you need to use your right foot to steady the bike.
Incidentally I had a really excellent ride around on the Banbury Run in the company of Andrew Nahum who was riding a Flyer that I once owned. 2 Speeders for ever!
I believe Titch’s old 2 speeder is in the Brooklands Museum, but I understand that his hand control modification has been discarded, and the bike has been returned to normal 2 speeder configuration. Rather a pity!