So your plan is to book US-EU as a one-way mileage ticket and book a separate EU-US-EU ticket? That should work to get you back into the US. How you end up using or not using the US-EU flight coupon(s) of the EU-US-EU ticket is up to you. The risk that AA goes after you as an individual passenger for this kind of practice is very low, but it can be made even lower.

I have had lots of Europe-US-Europe tickets where I sometimes haven’t made use of the entire ticket as originally booked. I haven’t had any problems because of that.