Put a few upside down and backwards. If you're very unfortunate and have to pay taxes, send two or three party check. On top of paying with a third party check, pay one of the dollars you owe in cash. When an extractor receives cash, no matter how small an amount, he has to take it to a special desk and fill out of few nasty forms. Any letter received has to be read and stamped regardless of what it is or what it's on.
Big envelopes have to be torn and sorted differently than regular business size ones.
An added bonus to the big envelope is that they take priority over other mail, so the workers can hurry up and deal with your mess. If you send two checks, they'll have to staple your unsightly envelope to your half destroyed form. Any foreign fasteners or the like have to be removed and put away. Any signature has to be verified and then date stamped. These methods are ONLY recommended when you OWE money.