The issue of sharing Superchargers has been raised here before along with a number of ideas to contact (or penalize) owners who leave their fully charged cars plugged in while others wait for a spot to open. Personally, I don't mind being contacted and moving my car if it is sufficiently charged and someone else needs a charge to get to their destination. However, I'm not fond of the idea of leaving my cell phone number on my $100K car for the world to see. While the solution I came up with isn't perfect, it does facilitate this communication while maintaining an owner's anonymity. For one thing, owners have to have the smartphone app for this to work. For argument's sake, let's assume most Model S owners use the app and opt-in to use this proposed feature.
Let's say you pull up to a Supercharging station and all the spots are occupied. You launch the app which uses your phone's GPS to determine that you are at a Supercharging station. Through it's connection to Tesla's servers, it also knows that all the operational Superchargers are occupied as well as the owners of the cars plugged into each station. Meeting these two criteria would enable a new option in the app: the ability to send a message to the owner(s) of car(s) that are fully charged, asking them to move so you can charge. If no cars are fully charged, you can send a message to all owners currently charging and ask if they are charged enough to get to their destination and wouldn't mind moving. These messages can come either as a notification in the app or as a text message. Since Tesla has all our info, we should be able to have a dialog with other owners without knowing any of their contact info. In addition, since Tesla also knows the status of the Superchargers and our cars, we can communicate with other owners without knowing the state of charge of their cars or in which spot they're parked. Let's say for one reason or another, I don't acknowledge a message asking me to move my fully charged car. No one would know that my black Model S on the end is the one that's fully charged, further preserving my anonymity.
Note that this can also work at public HPWC stations like those at malls with a Tesla Store. While Tesla may not know the status of a HPWC, the app can determine the owner of the car in your proximity that's plugged into a HPWC.