Does the Civic suffer the warm-up penalty, like the Prius? If not, he might squeak out a few more, because it's consistently warm in SoCal. If yes, 40 seems about right. At those speeds, the car's not going to do much better.

Patrick, keep in mind, the EPA tests for highway efficiency never exceed 60MPH. It's not a real-world test, so you can't expect to get that kind of mileage, in the real world. Check the mileage database for other drivers in SoCal.