I think on this occasion you may be a little too optimistic on how much BA can do for you. However unfair it seems, you will probably have to do the legwork to have any chance of getting the miles credited to where you want them.

I'm sure you've already realised that the fundamental step is to get AA to de-credit and release the miles back into the pool. Only AA can do that, and only on your personal say-so - they can't just take BA's word for it. It's not that BA doesn't want to fix this for you - they probably can't.

If you succeed in doing that, and it's by no means certain, then you can re-submit a retro-claim to BA.

In retrospect, wonderful thing that it is, when trying to do something like this on a single PNR the risk of it going wrong is sufficiently high that it's probably better not to put FFP information in the booking and then retroclaim the individual sectors afterwards.