Bit of an odd situation here. I'm booked to Norfolk Virgina flying from LHR to JFK on BA metal then on a BA code share on AA metal. There is only a single BA reservation reference for this flight, no AA reservation number.

No one appears to be able to book a specific seat for me on the BA/AA code share flight. I can't do it online on the BA or AA web sites, BA via the phone can't help, it just appears to be impossible to do.

I often fly via AA on a BA reservation, but more often than not these sectors will be under an AA flight number. In these cases you get both a BA and AA reservation, but this is a BA flight number on AA metal so only a BA reservation number and nobody appears to be able to change my randomly pre-allocated seat!