I’m planning to hike the JMT SOBO in July. My hope is to park a vehicle at the Whitney trailhead, so I can hike back to it.
tumblina
check to getting to/from trailheads on this website. that site is full of a lot of other info as well.
basically, hitch down to lone pine from whitney portal. that is where every car leaving will be going so it should not be hard. last year it took me about 15sec. to find a ride for three of us. from lone pine you can do two things. take the crest bus to lee vining and then the yarts bus to yosemite valley.
the other option is to hitch from lone pine to lee vining, which is highway 395 all the way and it is the only main road north up the ownens valley. then hitch down tioga pass road to yosemite valley. those two should be a pretty easy hitch as well.
jerm
You can park your car for extended time periods but you will need to insure that you leave absolutely no food or other items resembling food or with odors in your car or you risk a bear problem. You would also be prudent to not leave anything that humans might want to take either. I left my truck at the trailhead last summer with no problems. I also got a ride to Lone Pine with the first vehicle that came along. I took the buses but many others hitch a ride to YV.
Dave