You could always run a capacitor with your (smaller) battery tied into it. I did this on my neighbor's CB360, using the stock wiring harness. With both in place, the bike could be kickstarted with both head and tail lights. I switched the tail out to an LED unit to reduce draw and planned on doing the same with the T-signals. Right now it's still running smaller non-LED signals.
It's a bit redundant, but at least my neighbor can still run his bike if the battery ever craps out. Unless he turns on the high-beam, turn signals and his brake light while using the horn at a standstill......
For the record, I used a 12v, 2,000mAh (2amp) camcorder battery from Radioshack. The battery cost me $2 on clearance.
Edited for cleanliness