I guess you could dilute the Iron X and it might still work? I think it would be hard to tell though and if you're going to decontaminate a car might as well just go for it.
Another option would be to use the Iron X Snow Foam is you have a foam gun or just use it as your car wash soap.
Here's some more Iron X pictures from an all original 1990 Corvete we washed here at Autogeek over the weekend. We're going to use it for a Thursday night project car and I wanted to make sure the paint was not contaminated before the buffing starts.
Car Wash Day at Autogeek
More pictures in the thread.....
Car Wash Day at Autogeek