You have choices to charge on the way home from Rancho Cucamonga. I would just display the occupancy information on the touchscreen and monitor it as you head north.
I do not know your battery size, but with our 2014 S85, Tejon Ranch to Fresno is easy. Rancho Cucamonga to Tejon Ranch is easy. I have done this many times. You could also hit Santa Clarita instead and make it home in a M3 LR or quite possibly a Model S100 if you are a little careful heading up the Grapevine.
Taking Interstate 5 and utilizing either Buttonwillow or Bakersfield - West is out of your way a bit. But they would come in handy if there is major congestion at Tejon Ranch. With 24 stalls available at Tejon Ranch, I would think that turnover would be fairly rapid.
Just keep the occupancy information visible on the touchscreen!