Yes, it would be possible to do that, but it would require a solenoid switch similar to one used by Ford between the battery and the starter. You could engage the gear drive and press the button switch on the starter, then push a starter button to power up the solenoid and send the battery voltage to the starter. The burning question would be "WHY?"
Jerry
Something like
THIS Google> STARTER SOLENOID RELAY 6 VOLT
If you keep the original 6 volt battery the relay you use will have to handle a lot of amperage.
Or Puff the magic dragon when you push/turn the ignition switch/button.
You could hide it under the cab where no one would see it.
You don't need the amp wire in the pic.
