i think if you try to add 2 snippets of code (even if one is from another user), then only one will be displayed....i feel like i tried this at the beginning....
It is agsinst their terms to display more than 1 ad-unit per page. You also cannot create 2 accounts as they require a SSN number for tax information in order to recieve your payment. So submitting the same one for 2 accounts you will most likely get caught.