Ah! Thanks ukdoctor - I knew I'd seen that thread before but I was searching under MBNA Companion Ticket instead of AMEX.
I should have been more specific in my original post - I am only looking to upgrade the outbound DXB-HKT leg. My BHX flights are 2 class and we're not fussed about upgrading from HKT as they don't have an EK lounge.
I had the option to upgrade the return HKT-DXB companion ticket last week so I think it is possible - is it likely that ExpertFlyer is wrong and EK may release more seats at a later date?

Thanks for the replies so far.