Yes at checkin you can do everything individually because you are using the airport departure managment system. The reservations system can only process upgrade requests for the entire PNR...all or none. But the DM system treats everyone as individuals from checkin all the way up to the gate for standbys and upgrades.

Curious though... why are you "stuck" in this PNR? You can call UA and have yourself split off into a separate PNR and then you can get yourself on the UDU list earlier for the rest of the itinerary.. you can even split you and one other person off into a 2 person PNR and you can upgrade them with you. At minimum they could sit in E+ with you.