I have a NW program number I set up to be able to log in when booking on NW. Never collect miles in it, but just make reservations through it. Then during the booking (or after) you can add a new program (CO) to the reservation.

After I originally qualified as silver a few years ago it took several weeks for the status change to make it to the NW system though. I don't know if that's changed or not. I ended up having to have OP call NW after a few weeks had gone by.....