Just posted this in the 911 forum, here is the link to the DMV website and the form "Statement of Facts" and print out the PDF (form REG 256). Attest that the car is out of state (one of the boxes on page 1). I'd send it in as a double sided form, which is what DMV/AAA gives you.
A friend turned me on to this and he said he did it a few years ago and has never gotten a registration renewal requiring a smog test. Says he does it for all his cars, so no smog check or smog certificate fees again!
Here's the link.
http://www.dmv.ca.gov/forms/formsmost.htm Go to "Vehicles" and then "Statement of Facts"