Thanks for all the help, everyone. I'll give BA a call and see, which I was planning on anyways... just wondering if there were any ducks to get into a row first.

FWIW it's not so much a mobility problem, and he's probably the only one that enjoys long walks in airports to stretch his legs, it's once he gets settled for 30+ min, it stiffens up, so it would be good to only have that happen when he needs to get up not both him + his seat opponent.