Don't smoke, eat, drink, let pets or young children ride in your car and it will stay a little longer. You could also keep the windows and sunroof closed as much as possible. Its been 6 months for me and I've still got it!
And don't volunteer to take your new car on a road trip with three other guys to a college football game
Feeling like a geek, I had golf towels in each seat when the guys got in, and told them what they were for. After morning #1, new car smell was still there. After morning #2, new car smell was long gone - or simply masked by three large beer spills. Cleaned them up when we got back, and everything was fine.
Oh, and the towels I so thoughtfully laid out for my buddies. NEVER used.
[...] i believe once it's gone, it's gone, hence why it's called the "new car" smell...
I will second that. Whatever the auto supply stores sell that claims to give off that "new car smell" is anything but. Something in the car's insulation has a great deal to do with the car's ability to retain that odor. My 1959 Buick STILL has that smell every time we get in. We don't smoke or eat in her either, FYI.
Patrick [aka: The Oracle]