As far as I am aware, there is no provision that allows you to ship the rifle to him, even though he is the owner. Since it is crossing state lines, it must go to an FFL.
I know this is going to sound weird, but there is absolutely nothing you need to do, legally speaking, to the rifle. Send it to the FFL, and let the FFL and your friend worry about making it legal for transfer in that state. You are not bound or obligated under CA laws. As long as you have shipped it to an FFL, even if in "evil" configuration, you have done your legal part.
Since it is your friend, the only thing I would do is make sure the FFL can transfer the rifle due to the name on the receiver. If the brand is banned by name, the FFLs hands will be tied. In that case, you can sell it for him and send him the money, or your friend can list it on gunbroker or some other means of classifieds, while the FFL holds the rifle, and when the rifle sells, the FFL can ship it to the buyer.