I've got myself an upcoming Aer Lingus flight from BHD-LHR. Not a codeshare.
Did discover that you can check in from 3-30 days beforehand and I can enter my BAEC number during the check-in process. Doesn't seem to do anything as expected although might get 78 Avios or whatever trivial amount.
Can't go too far as I have to purchase a seat if I'm checking in more than 3 days before departure (€14.99 for an exit row down to €7.99 for a normal, non first 6-7 rows seat).
Sure I can survive an hour in my allocated middle seat in the back row