I've always been able to select a seat through my corporate booking system when I book in Y for flights to GLA - before I confirm the flight, I can bring up a seat map (and try and guess how many business rows there will be, so I can nick the snug...). Only works in Y though - if I try it in E, for instance, I get told that no seating info is available at present, even when I can see it when I select a Y ticket.

Whether it's meant to happen or not is a different matter, but it's definitely possible!