For the Factory NPP there is a fuse you can pull to keep it on the loud side. That's what I did and I will never go back. It does cause only one side to get dirty on your pipes which is one way to confirm that the flap is staying open.
There is a DIY guide on the forums, but I doubt its the same for a retrofit.:
http://www.camaro5.com/forums/showth...=npp+fuse+pull
You might need a mild to wild (or something like it) switch for it.