I just had an interesting thought cross my mind...
Currently on a trip where they paid full-fare J for me ($11k r/t, painful!) - on my way back from LHR-YYZ, that segment alone was $3,700. Can I get them (at the airport, LHR) to downgrade me to M, use a cert, and then get an MCO for the $2,700? Or would they have to refund fare difference to the travel agency.
Anyone ever done this? I'd prefer to salvage some of the value for myself