Originally Posted by
bealine
Imagine the flight from A to LHR does not give sufficient connection time to Y and there is only one flight a day (or less) - imagine somewhere like Entebbe to Split (I have pulled those out of thin air - I don't know whether they would connect or not!).
So, the OP wants to book A to LHR to X (maybe Frankfurt, Madrid, Paris etc where he could book an evening flight secure in knowing his BP scan would pass conformance) and then proceed to the Boarding Gate for Y (Split) and persuade the staff to check him/her in.
I must admit I hadn't considered that scenario, the impression given by the OP is more that he wanted to have his lounge access cake and to eat it, but he is hardly alone here in being unnecessarily mysterious about it all, and indeed that is his fair privilege. The easier way to handle your scenario is to book a separate ticket, but the points you make about its viability are very good, and in particular that the TRM - who has to balance a whole raft competing pressures but with an overriding sense of getting the aircraft out on time - is rightly going to be biased against any last minute wrestling with Ready to Fly or FLY just to suit one passenger's requirements.