There’s a library available that makes it really easy to lock and unlock Storyboard levels in your Corona SDK games.
You can find out more about the code and the tutorial videos here:
http://masteringcoronasdk.com/ogt-level-manager/
Jay
PS - When the public release of Composer happens the library will be updated for that (free for existing users). You’ll be able to use OGT Level Manager with Storyboard or Composer.