Another option is to book an Amtrak ticket one way from SAN to OAK.

The train station is within 4 miles of SAN and the train takes quite a scenic route. Your friend would have to transfer trains in either Los Angeles, Santa Barbara, or San Luis Obispo to the train continuing to San Francisco/Oakland.
The train stop in the Bay Area is Jack London Square in Oakland, and a bus/shuttle is offered to get to the Trans-Bay terminal in downtown SF.

I did this once back in '87 or '88.