Put this in your app delegate.
[[NSUserDefaults standardUserDefaults] setObject:@YES forKey:@"UIUseLegacyUI"];
[[NSUserDefaults standardUserDefaults] synchronize];
You'll need to restart your app to take effect :)
Did you submit an app with this code?
IMHO, it probably will not be acceptible on the AppStore due to use of private and probably future-unsupported API.
No I didn't try, and as you said I don't recommended this for production use. However it's useful to preview your app back in iOS 6 environment on iOS 7 devices/simulator.