I already tested it.
Unless some one can come up with a way to very efficiently boost 10 to say 48v up to 383ish volts and activate the obc there isn't much point.
Boosting the 12v system with external power does almost nothing. It would be a lot of work to get maybe a 1% boost in range.
In park, no external lights, no heat or AC, pumping 14.6v into the battery at 12 amps it would reduce traction battery draw less than a half amp.
A grille block, brake pad drag reduction clips, reversed mud flaps even if your car didn't have mud flaps and bought them from a dealer to butcher, pizza pan style hub caps, would be cheaper and more effective.
The only way boosting the 12v system could be noticed is if you drove the car a lot during the day, city driving and could cover most of your 12v heatpump blower and condenser fan load with solar.
2011 white SL leaf with 2014 batt.
Chargers: Panasonic brick moded for 240v, duosida 16a 240v and a 10kw setec portable CHAdeMO