I did the C gate express to get out once for similar reasons. It was extremely difficult to get back in as the BA system considered me still to be airside. It was preceding the last flight in an ex OTP to PHX, I forget the exact circumstances and why I didn't just exit and go back in rather than transitting, but it probably had something to do with breakfast in the CCR, Anyway it took a good 25 minutes to sort out in the F wing and I wouldn't willingly repeat the experience.