If it's only a tailpipe sniffer test and they don't open the hood or check for any emission pieces, there are vehicles with smog devices removed and in tune that are far superior at passing a shiffer test than a brand new car you've drove off the lot.
If it doesn't run rough or have any engine related drivability problems, I'd take a nice drive for about 30 minutes where you're up to speed on a highway to get the engine nice and warm and at a consistant burn rate, then pull over somewhere and grab a burger and fries and let the motor cool down for a while, then pull the plugs on it to see what condition they're in. If they look right (a slight tannish color) I'd just go try to pass the test and if you fail, ask for a printout of what you failed on and then go from there. If you're not sure how to read plug, every Chilton's of Haynes manual has color pictures with descriptions of what different conditions of plugs look like.