When backpacking in the Sierra you'll quickly notice that the JMT draws a crowd - lots of people on the trail, at the crossings & lakes, and in the trailside camping spots. Every side trail is refreshingly less populated, and there are countless loop opportunities. So unless you are fixated on hiking the whole JMT to tell everybody you did, there are better options. The North Lake - South Lake loop, mentioned above is one. Something out of Mammoth involving Thousand Island Lake and maybe Isberg Pass is classic. Something from Horseshoe Meadow mentioned above. Rea Lakes loop with a side to Sixty Lakes Basin. Something from Onion Valley going over Kearsarge Pass and looping on the other side. Or Something out of Mineral King, my favorite area. Consider one of those and don't worry about having to shuttle or finding a place for your tent.