First, I would only park there if you really do need to charge, not just because it is a good parking spot.
If you have a smartphone, I think you can use the ChargePoint app to start and finish your charge remotely. If you complete the session this should unlock the J1772 connector. This would at least allow someone else to use the station if they can get access. If there is a nearby spot available, you could use one of these extension cords: http://www.greencarreports.com/news/1095906_electric-car-charging-statio...
This would allow the normal parking spot to remain open.
I would also put an EV card (http://www.pluginamerica.org/evcard) on your dashboard. This would allow someone to call you if they would like you to end the session or want to know if they can unplug your car.
Lately, I've been wondering what is the right protocol for me to use at public chargers. I may not always be right there to unplug once the car is fully charged and move it out of the way for someone else. And it's bugging me.