So I've got yet another upcoming trip where I fly into LHR on AA and connect to an outgoing BA flight. The thing that drives me absolutely insane is that extra security check in LHR and the disgustingly long line (most of the time) to get through it. Does anyone have any thoughts, suggestions or ideas on expediting that process? Or am I dreaming?

Also, can anyone give me some pointers on seating on the BA portion of the trip? I'm Plat, and traveling with a friend who's on a separate PNR. BA won't assign seats in advance, so is there anything I can do to improve our seating and make sure we don't get separated?