OSX Document Icons

How do you set a document icon for a standalone application in OSX with the Projucer? (A different icon from the Application Icon.) I’ve set the document extensions in the Projucer, and I cannot seem to figure out how to set an icon for a specific document extension. I have tried:

  • Creating an png named the same as the document extension. (added as an xcode resource)
  • Creating an iconset with the same name as the document extension. (added as an xcode resource)

Neither seem to work. Is there some magic I am missing?
Thanks!
Chris