set yourself up a micro-generator, a few small coils of wire, with a magnet set up on one of the spinning parts, a couple diodes to keep the power flowing in the right direction, tag that into the alternator feild wires, and the act of kicking will produce enough juice to get the alternator going normally.
Also, have heard of people setting up a magnet inside the alternator to excite the feild enough to start working.
You'd still need the cap though, as power would be pulsed, and the cap would/should smooth it out.
If you just want to get rid of the bulky stock battery, use a small pack of nicads or nimh batteries, friend had a setup like that on his bike, panasonic cordless drill 15.2v battery pack that he tore apart and mounted in a couple of tubes, worked nice, used a zener diode to manage charging on it.
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