Hitchhike?
One of the truisms of off-season Sierra camping and hiking is that transport can become complicated. Services can be limited before and after the normal season. Without that bus tour to GP, he might need to bring a friend who can drive the car down from his start point to the bottom. Or modify his plan - perhaps change to a circle hike that starts and ends at the same point.
I don't know what else to suggest. I did a lot of solo hiking back in "the olden days" so am familiar with the problem. It can be frustrating.