We had a different situation than you last year. We left a car at Portal and then got a ride from a relative to the valley. When we finished the car was there and we got out nice and quick. I do not know where to park in Lone Pine, however, if there is a place you feel safe, it would be easy to leave the car, as noted in the post above, and take the Yarts into the valley and just hitch to Lone Pine when you get back.
The shuttle service from Portal to Lone Pine would be nice because you would have a place to leave your car in Lone Pine.
If it were me and I had time, I would drive up to Portal, leave the car, get a ride down the hill and then take the bus to the valley. When you get off the trail it is nice to have your car right there to get out.