I am driving a friend's vehicle and his registration has expired; I've agreed to pay on his behalf, but am precluded from doing so on line, can I come in to pay at your office?

The owner needs to be present.

My understanding is you have to be a AAA member to renew a vehicle registration at a AAA office. Also I would think the owner of the vehicle will need to be present, unless that's you. If you're paying on behalf of the vehicle owner, you can pay directly to the DMV by mail, using a check. Just make sure you reference the vehicle's license number on the check, and include the vehicle registration renewal form with your check.

It would be a lot easier if you just do it online

If you have the DMV paperwork and it doesn't say Smog on it. Also cash or check only

I think the owner has too go into (AAA) and pay the registration at member services or the dmv.

Yes