Just my opinion, and I have not read the rules closely, but if you book part of it as an Iberia ticket and the other part as an AA ticket, you would actually be within the rules. There might be some complications with earning mileage, but my opinion, which could be incorrect, is that AA has little say as to what you book on another airline.

As far as AA should be concerned, I think, would be that you are in Italy, you want to fly to the US, and then return to Italy. As far as how you got to Italy, and how you plan to return later (IB), is not within their purview.