You can provide whatever info you want on the second mailing line (e.g. Apartment A, Suite 100, Floor 2) and you have a unique shipping address.

I have 4 credit cards. My dad has 23. I had a friend who had over 100 when he was loading up airline miles. Let's not forget anyone can go to walmart and pickup a visa/amex gift card for a unique identifier.

And I thought of this within 30 seconds of reading your post. Imagine a dedicated scalper..