From
here:
What if I lose my PIN?
If you lose the PIN given to you by a credit bureau, send a letter to address on the sample letter attached to this sheet. Explain that you have lost your PIN and would like a new one. Provide your full name, address and Social Security number in the letter. Enclose a photocopy of your driver’s license or other government-issued photo ID.
Based on that, wouldn't it be fairly straightforward for someone to make a convincing enough fake ID to convince the credit bureaus to reset one's PINs?