There's an infinite amount of ways you can rig this up to work...
you could modify your old bing 'elbow' which might work, or you can just do what I did, which is kind of shoddy but has held up for hundreds of miles with no problem...
I took some wire, and after pulling the cable out a bit I wrapped the wire TIGHTLY around the cable a whole bunch of turns and then electrical taped it. You have to play around a bit to get the length right cause you want it to be fully closed and have ~1mm of free play in the throttle, but then it also has to get tight enough to open far enough...
If you don't want to rig something up, I think 1977 sells a long pull throttle assembly that would work for a more permanent solution...
I've also heard of people using cable stops or even soldering a clump of solder onto the cable as a stop... which I'm kinda leary of.
Anyway hope this helped... Somebody else will probably have a better solution but that worked for me!!!!!!!!!!!!!!!!!!!!!!!!!!
PEACE good luck