I am afraid not, at least not online, unless it is some time off, since Aer Lingus (EI) is at least 6 months away from joining oneworld. Your status doesn't work on that service. Given that it's a short flight on an A320 or a Stobart ATR-72 I don't think it makes much difference, but you can ring up Aer Lingus and get a seat allocated, if booked under a BA codeshare, since EI regard that as a Plus fare with advance seat allocation. However the seats available won't include the seats with extra knee room, the rest are all the same.