Edit doesn't "bump" the post. DOH! Please see the "BUMP" bit in my post above.
EDIT. I found a way to use "nvnalllevels" at Demon Crusher. Keep a save at MoC difficulty. Play the first two chapters on DC. It's probabaly safest to exit and restart the game, at this point. Load an MoC save. Use "nvnalllevels". Load a DC save. Go to the Main Menu and choose "Challenge Rooms". The Chapters should be unlocked and whichever you choose will be at DC.
I'd still like to play the flight levels at some point, though
