You bet!
If you aren't on the same PNR, just call the MVP Gold line. Even if you are, some times it doesn't give you the option to UG since everyone on the PNR is not MVP Gold. Guess a quirk in the system.
BTW - Two days ago I called to UG both parents traveling with me. Of course, I first verified that there were three FC seats available. Used companion for one and upgrade coupon/cert for the other. We are in FC PSP-SEA and SEA-PSP. The flights are all around Christmas/New Years. I was pleasantly surprised. The CSA could not have been more helpful
She knew exacttly what I wanted to do and made it happen! Now that is customer service.