I see a lot of those old exercise bikes people used to use with the old school speedo's on them. You know the kind that had one front wheel ? I don't know
if the cable would reach to the handelbars on your bicycle or not, but I've seen these things in yard sales for a couple to five bucks. Some just free to a good home. If the cable doesn't reach to the handlebars with enough room to turn, then perhaps mount it to the frame head tube somehow.