Whitney Portal has the easiest shuttle service in the Sierra: your thumb. In fact, you probably won't even need that. I was offered a ride before I finished my burger at the Store, by people sitting behind me whom I had not even met. and I pretty much looked like Freddy Kreuger after finishing the JMT.
Depending on your hike route, you can probably line up a ride from trail family before you even summit Whitney. Start talking about it to people you meet around Crabtree. That'll at least get you back to town, and maybe back to HM.