I use the Tesla mobile charger (the one that comes with the car). If I have my smartphone with me, I can press and hold the button on the charger handle for a few seconds. You'll hear the car wake up and a second later release the charge cable. The color of the Tesla logo, where the charge cable plugs in, changes too.
So, it takes a few seconds, but yes...you can release the charger cable without getting in the car first.