Basically, you fly over there, show up at the factory, you get treated like a dignitary, they show you "baby pictures" of your car being built, and then you drive off with it and get to cruise around Europe for 30 days. When you're done, you drop the car off at one of a half dozen ports and fly home. Your car arrives a few weeks later.
You get about 10-15% discount and it's a very cool experience. A friend did this for Porsche and while the car was great he said the experience was a little lacking. That they do such lower volume they didn't have the program as perfected and it was more about just showing up and taking possession of the car.
Anyway, that's obviously not what Tesla is doing -- but they should. They should definitely have a California Delivery program. They probably already do.