Open the Storyboard file on Xcode 5, And then:
1. Open file inspector
2. On "Interface Builder Documents" section change "Open with" to Xcode 4.6 (if it's 5.x).
3. Save, Close the project and open that with old Xcode.
It should work now.
This is same method like on earlier releases so I assume that's ok for NDA case (you can do the same thing on Xcode 4.6 to work with older version).