How bad did you flat spot them? If they aren't way too bad (cord showing etc.), then you might be able to put them on the rears and keep on racing. If the vibration isn't too bad, the biggest problem is in braking and the fronts do most of the braking.

Flat spotted tires tend to skid easily on the flat spots again. Rears rarely lock which is why you might be able to run them.

#37 ITB