Just run the big wire from the alternator to the battery an leave your amp gauge wires where they are. The gauge still reads a little but will never deflect much.
For my power top and power windows, I used a relay from a late model convertible and power top motor with a single winding instead of dual windings used back then. I ran a big wire to a fuse block in my trunk then power my tope and rear windows from it. The only power switched through my top switch is to switch the relay contacts. See my Pace Car thread for a pic of the relay, pump motor and fuse block.
Andy, You can't get to the back of the gauges easily once mounted in the car. Easy to hook a battery up while on a bench.