I agree with Greg on 300.5, as concrete is more of a continuious material, and more "permenant" in a sense.

However, I have SEEN RNC laid to about 6" below paver bottoms and also have seen it pass inspection. As far as "drilling out" the pavers, I'd have to question the logic in this, if I'm getting what you mean.

If acheiving a 12" depth is an issue, you might have to bite the bullet and inquire with the AHJ as to how he inturprets 300.5. A screw up here could cause a re-do, and nobody wants to work for free!

Good Luck!