Hell, take out all of the seats except the driver's seat. It doesn't take long.
Pull out the glovebox
Empty your washer fluid resevoir
Run on a nearly empty tank of gas
Don't forget the parts associated with the spare tire - wrench, jack, etc.
Make sure your tire pressure is correct
If you drive your car a long way to get there/it is hot outside, ice down your intake before your run
Take off any skidplates
Leave your A/C off, windows up
Remove nerf bars/fog lights/roof rack if you have them
Unscrew your antenna (is that possible?), leave your mirrors folded in (not sure how much of an effect this would have)
Remove as much interior paneling as possible - pillars, door panels, etc.
Take out the floor mats
Wear as little clothing as possible, be sure to use the restroom before your run (empty your bladder/colon).
That's all I can think of for now. Hey, every little bit helps!
