The DOT prohibits use of Run Flat tires without a tire pressure warning system. It's a good rule, one that shouldn't be ignored.
The Z has the TPW system, but it is disabled. You'll need help from your local dealer to enable it with their Tech-II scanner, and you'll need to buy sensors for all four wheels.
You don't need to use Run Flat tires to use the sensors, I don't.
The handling properties of the Run Flat tires are a bit different from normal tires due to their much stiffer sidewalls. Personally, I wouldn't mix them with normal tires. Also, the Z mounts a 295 in the rear. As far as I know, the largest Run Flat you can get is a 275, which is smaller than stock (it's the stock size for the Coupe and Vert).
If you want piece of mind, just install the sensors. Tires rarely go flat instantly, they leak slowly. With the sensors, you'll always know how much air is in each tire, and the system will warn you if the tire goes below, I think 24 PSI, so you can just put more air in the tire (your Z comes with an inflator) until you can get repairs.