You have to make sure that your AAdvantage number is in the reservation. Unfortunately, no way to do this on BA.com. You can call BA, or you can pull up the reservation on the Royal Jordanian site (rj.com) using the BA PNR and change it there. If the AAdvantage number is on the reservation, it will credit to AA.
Cheers.
The advice on the BA forum seemed to lean towards Finnair.com, which worked seamlessly for me, booking a BA Holidays package under my Executive Club number, then changing to AAdvantage FFN for credit/elite benefits some time later. Interestingly, I still got the Bonus Avios from the package booking after travel, despite having changed the FFN. Postings in the BA forum suggested that this wouldn't happen.
I also found in my searches that some packages imply a lower ticket cost than you can buy on it's own, unless you impute an improbably low per night cost for the hotel portion, although my experience with a close-in booking was that there was no discount, effectively, and I probably should have just booked separately in order to realize hotel points as well.