Okay, here's what I found:
"
Private party purchase for out-of-state use, one-trip permit
The purchase of a vehicle from a person in California, who is not required to hold a dealer's license or a seller's permit (private party), is generally subject to use tax at the time the vehicle is registered with the DMV. However, a purchaser is not required to pay California use tax if the only use of the vehicle purchased from a private party in California is to remove it from the state and it will be used solely thereafter outside this state. This exclusion from use tax requires that no other use can be made of the vehicle in this state. A One-Trip Permit may be issued by the DMV in lieu of registration, for operating certain vehicles while being moved or operated unladen for one continuous trip from a place within this state to another place outside this state. This exclusion does not apply to sales tax."
So, if buying from a dealer, the vehicle would need to be transported by a shipping company. Otherwise if from a private party, the buyer just needs a one-trip permit.
Source: CA Board of Equalization (page 10):
http://www.boe.ca.gov/pdf/pub52.pdf