[Sluttypatton]

1) Do a complete engine flush (formula 1 makes a decent engine flush, so does AMSOIL).
2) Put in some fresh (cheap, as you are gonna drain it soon) oil and a new filter, run the car for a little while, drain that oil and put in new oil and another filter.
3) Check your pcv valve to make sure it is functioning properly.
4) Retard your ignition timing before you get tested, and when the testing is finished correct your timing.
5) Make sure you have a functioning catylitic converter, and emisions control system.
6) Never tried this but if your really desperate to pass, try placing strategic exhaust leaks upstream of the tailpipes...not sure if this works though as I think they test in parts per million, exhaust quantity may not make a difference.