I think I can.

Instead of registering, just login to your gold circle account, or rather use your gold circle credentials to log in to the Aer Lingus site. I cannot recall exactly what happens next but it is along the lines of being force migrated to Aer Club, and asked to create a username for your Aer Club account.

You should at the far end of this (short but somewhat confusing) process find that you were in fact pre-registered for Aer Club back in November and your 250 avios will be waiting for you.

I did this myself just the other day so it should work for you. Please let us know if it does.