I believe you can register cards to 'automatically' receive the bonus miles.
From the UA shopping mall it says:
Register up to five credit or debit cards to automatically earn award miles by shopping with participating retailers. Please allow 48 to 72 hours in order for your card to become active. Once your card is in active status, it is eligible to earn.
I'm not sure how that works, maybe its for in-store purchases?, or automatically applies the portal bonus?, someone else more knowledgable can chime in.
What I DO know is that you can double-dip by receiving 1xUR/$ and whatever bonus that the AA portal will give you.