While I may not be an expert on aerodynamics, I do think that Tesla can get the Cd from .36 to .31 quite easily without going into boattails. Remember that these guys have access to all sorts of resources that us commonfolk can't get (might be an exaggeration, but still) like engineers and lighter materials. .36 Cd is fairly high, so it shouldn't be too hard to drop it 15% since it is already pretty high. Just look at Metro's 15 mods for 15% improvement and you will see that it is pretty simple to get improvement from a stock car.
I reckon that they will add an air dam, smooth the underbelly, add tire spats, and maybe get a new spoiler on that thing.
__________________
|