If software patents were around back in the 80's
They were. Commodore used a character set which contained an inverse-video duplicate set to avoid a software patent on the use of exclusive-OR to draw a cursor. Specifically, some drafting company back in the late 70's patented the idea of using XOR to draw a crosshairs, so in the VIC20, C64, and others, the cursor was implemented by periodically alternating the target location between the character located there and its counterpart in the inverse-video half of the character set. Apple avoided this patent by alternating between the character on the screen and a little checkerboard cursor.
obligatory: http://xkcd.com/941/
So put a big, obvious indicator on the charging station that shows a color-coded load level. After a while, EV owners will come to understand it at least enough to know that a high reading means their car will charge slower.
If consumers can figure out those little pinch-the-ends-to-read charge indicators in some batteries, and what a regular traffic signal means at an intersection, they can figure out "green means fast, red means slow" at the charge station and charge up or go elsewhere accordingly.
Stations can even display their capacity reading on their main sign under the price, if they're proud of it anyway.
Impossible. Who would bother dragging the mime's invisible box into the carpool lane in the first place?
Make sure your code does nothing gracefully.