Join Date: Jun 2004
Location: Northern Nevada
I think you need a new bike shop, or at least an explanation of why that's a bad idea. I have an old Trek that started life as a triple-crank tourer, then did five years or so as a five-speed around town (I took off all but the middle chainring), and now is a singlespeed. Unless there's something really unusual about the setup you plan to use, I can't think of a possible problem.
If you don't have a shifter for the rear, you don't need a five-speed index shift lever. Any old thumb shifter or friction lever or barcon will work.