In practice I haven't had a problem with checkin ever, I (status passenger) just say I am travelling together with my companion on separate reservations. The CW bag drop (zone H) is usually as fast as F bag drop (or faster!) and not carefully checked, so just go there.

I rarely have a problem with Fast Track either, non-status passenger boarding passes won't open the gate but then status OWE (non-BA) passenger boarding passes won't open them either - so just tell the human gatekeeper that you're together and he/she should scan both boarding passes and let you through.