I drive too far to do without an alternator. And my drive home is at night so I need the lights on. I could do a switch.
Ideally, a 3-position switch: Charge, No Charge, and Auto.
Auto position would do as has been discussed: charge when brakes are applied. I would add to that, charge if battery gets below some voltage and charge if throttle is below some position. Add a switch for throttle position and a voltage comparator. Adjust switch position and voltage for best results, whatever that is.
Shouldn't be too hard to do.
And then I guess I would force Charge 10 mins from home to make sure I can start the next day? Or, better, connect battery to a charger during the night.