Back in the good old days on the farm when you wanted to jump off an old 6V tractor or combine with a 12V we just hooked a jumper wire to the frame and hit the input wire of the starter with the jumper cable so there wouldn't be any feedback through the regultor or cotout. FOf course the only gauge back then that worked off of electric was the amp gage which wasn't effected anyway and the starters were Autolite which didn't have to have the Bendix pull or pushed in. If you have the bendix pushed in on the starter when you hit it with a light duty 12V battery there should be enough voltage drop from teh battery and jumpers to where there shouldn't be any damage to the regulator as long as you get off of the connection immediately after teh engine starts.
