I know this sounds incredibly stupid, but do you think you can use a smaller car alternator for bicycle lighting? (lets just say for the cool factor...for that chopped up cruiser bike you've been building..you know...short trips)
Spinning an average alternator by hand doesn't seem to produce much drag to me, but this is when its completely disconnected. Maybe you could run one much like a bottle dynamo.
I suppose you could vary the field coil voltage to get more power on command or less drag, depending on the time, maybe by turning a knob on your bicycle, or to have dim/bright lights. Maybe even a large 6 amp headlight!
Also also...what if you used some super-capacitors and an average 6 volt bottle/hub dynamo to run high current device for a short period of time on your bicycle?
... such as a horn. more specifically, a vintage 6 volt "ahooga" horn.
slowly charge the capacitor, watch voltage and amps go up on cool vintage guages on your bicycle, and honk the horn to scare people every few minutes!
anyway...late night ideas.