We had some major general parking issues at my work a couple years back. There were barely enough parking spaces, but if you showed up after about 8:30 you have to park out in the boondocks. We ended up with a lot of illegal parking to avoid a ~500 foot walk (horrors...). People were parking in front of fire hydrants, up on the grass, and in ways that made it very hard to back out of legit spots.
A simple note got put on the windshields of the offenders:
"Nice Car.
Now please put it in a spot.
-Your Co-workers"
People got the message, and it did not appear to cause any backlash rage.
Perhaps a similarly kind note, printed out and ready to deploy, would help edjumicate folks?
"Nice care, but...
please do not take up the EV charging spots.
We need to charge to make it home.
-Your friendly EV driver"
I know that the "Eat my voltage" and "Do your gas dollars fund ISIS?" crowds will not approve, but a pleasant informative message is less likely to get your car keyed down the road, or cause someone to start blocking intentionally.