I'll go one step further and say that most line minders don't care about the BP, only that you can provide proof of your status. Back when UA and AC were sharing the A1 pier in EWR, I'd use my MP silver card to get into the elite line at security when flying AC, and the maroon morons wouldnt give me a second look. I think I also did the same at the D/E checkpoint in PHL prior to elite reciprocity between UA & CO.