To my knowledge it really isn't enforced. My wife and I maintained our main account with only the discs sent to our house.
Otherwise we later opened 2 digital only accounts and canceled them before each account hit the month marker.
I tried calling in to Netflix to get the bonus for being a loyal member (we've had them for 5+ years), and the CSR gave me a song and dance about AA being responsible for the promotion.
I doubt you'd be able to do the infinite renewal since they would likely limit it to one bonus per AA account.