Yes. Remove the aerodynamic aids on the car. They aren't going fast simply because of the gear stack or the motor. This is momentum racing - they are going fast because the (relatively speaking) don't have to lift (off throttle). If you can make the car dance in the turns at a much lower speed, you have a lot more variance of what speeds cars can get into the turns, what speed they come off of them at and you have a much more varied field.
If you simply want to limit speeds, limiting the gear ratios would work. It would however not be the best way to do so (pretty sure NASCAR restricts gear ratios anyway but that's not here or there). Along the lines of my above comments, you want to limit the speed a car goes down a drag strip or around a road course or an oval, the easiest thing you can do is change the limit of adhesion (i.e. bolt on some winter tires). Now going around Daytona (or really any track for these guys), the weight of the cars and the force they are putting into the tires, I don't think you can compromise mechanical grip by putting on a lesser tire, but if you remove the wing and aero and ground effects, you have effected the same change.
