Marla, if you are still looking for someone to share a resupply you might try the JMT group on Facebook as well as the JMT Yahoo group. Both groups are very active.
The JMT stretch between Whitney Portal and the Muir Trail Ranch poses real problems for people averaging less than 11-12 miles per day. Renting a Bearikade Expedition from the Wild Ideas guys and being clever in packing the canister can help. Most people take way more food than they eat, but hiking without enough calories is not a good strategy for most hikers.
Depending on the reliability of strangers for resupply seems dicey to me. I've heard multiple reports of people getting left in the lurch without their resupply packages. For some people hiking out over Kearsarge to Independence might be something for one to consider if limited vacation time is not an issue since it's only seven miles.
The Mt. Williamson lodging deal is somewhat pricey, but just paying $50 for them to hold your resupply might be a good option as the post office closes at 4:00 and is not open on the weekends. The other issue is that hitching a ride back and forth from Onion Valley to Independence could require several hours and a lot of charm. Offering gas money to passing campers could help your chances.