Find out which bank your mark uses and call them. Tell them you're away on vacation and your Aunt just informed you that your house had been broken into. The thieves took all of your banking stuff including your checkbooks, savings passbook, and ATM card.
They'll immediately put a "freeze" on his account and he'll have to go through extra steps when he tries to withdraw and money. If he writes a check it probably will bounce and if he tries to use his ATM card the machine will eat it and he won't get it back until he's cleared up things with the bank.
find someone who is a victim of a hit and run. Call the person or the police and make an annonymous report that you were there when it happened and you saw the license plate on the car. Give them your mark's plate number.
Some magazines let you use a credit card to pay for the subscription. Use someone else's card and when the owner of the card gets his bill, they'll investigate it and eventually narrow it down to your mark's address.
There's a couple more that are really fucked up.
Want 'em?