By forwarding the email receipts we get from Apple to a special address you could reserve for this purpose, a program you write may automatically scan such emails and update our accounts, not only with purchased status, but also with purchased date, paid price and iTunes order number.

Those of us concerned with our privacy may edit out our personal information, substituting our AppShopper account before forwarding. Or, you could make sure the emails are not harvested for personal info and discarded afterwards.