if you have a 1" threaded headset, you can rig up a "lightweight" holder by attaching a bottle cage to one of those heavy duty front reflector spacers. the most recent one that i've found looks like it could hold a bottle - made by cat-eye, threaded for an adjustment bolt, the whole shebang. works in a pinch, but would probably need more support in the long term. had it done on my bike as a kid, worked fantastically.