Make sure you send him on at least 3 trips to Western Union - The first one, explain that you got the name wrong. The second one, tell him that you forgot to hit "send" on the online account. If he still around, tell him that Your request got bounced.
Even better- try to fully scam him. When he sends you the fake cashier's check, tell him that you heard something about some "internets scam" and that you'd feel a whole lot better about the transaction if he would wire YOU $10 as a "good faith gesture" - then you promise to send him the cash left back on his phony check. If he's dumb enough to send you $10 via Western Union, go buy yourself a 12 pack.