Dan
Unfortunatelty with no contacts at LHR I wouldn't be able to assist on this one, not sure but Bealine may know someone.
As far as a Jumpseat goes, unless you hold a BA identity card it is highly unlikely that you will be able to use the jumpseat even for a chat. Depends on the crew on the day I suppose.
Anyway your best bet as far as talking to the flight deck would be to ask at check in, I have had similar requests although I am not sure if they have ever been followed up, again I guess it depends on the crew.
Hope this helps
Bluejay