I wired a little electricity power meter I bought on Amazon to my EVSE. I'm charging at work now that they installed a 14-50 outlet for me (nice boss I have, although it took a year of wheedling). I'm going to pay for my electricity. Boss says not to worry about it, but when he sees I've used 2 MWH of electricity after a few years he may let me! This is actually for my Volt, as I don't charge the Model S at work (no need of course). But you could easily wire one of these meters to a 14-50 outlet used for a Tesla to allow you to pay for your power used at work. The meter was about $20 on amazon. It has four connections - two for the current transducer and two for the voltage. Very simple to connect.