[shovel]

I really believe that beyond turning the magnetic field on and off within the alternator, there's really not much to gain here at all. I'm not trying to be negative, all ideas deserve some consideration. I just think the old saying "nothing's ever been so simple that some fool couldn't make it more complicated" applies here. Engage and disengage the alternator's field coil - or better yet build an arduino project that regulates the field coil's strength in conjunction with the alternator's regulator... and you've got all the gains you're reasonably going to get.

Then dedicate the rest of your creative energy to aero and weight loss.