It sounds like you want to start out with a bare UIViewController, containing your home screen with your own custom buttons.
The UINavigationController should come into play only when a user performs some action. Do this by
[navVC setModalTransitionStyle:UIModalTransitionStyleCrossDissolve]; // pick an effect
[self.viewController presentModalViewController:VC animated:YES];
Where navVC is the navigation controller, and self.viewController refers to your (new) main view controller. (add a suitable line IBOutlet UIViewController *viewController; + @property line + @synthesize line)
You need to fiddle a bit in the way the app starts up, for now it will probably show the navigation controller directly. If you are using a xib, you can do this by adding a UIViewController while leaving the navigation controller there as it stands. In application: didFinishLaunchingWithOptions: you'll find a line saying
[window addSubview:...];
which actually determines which viewcontroller's view is first visible. Change this to:
[window addSubview:self.viewController.view];
If you've done all this correctly, you've inserted the extra UIViewController between startup and navigation.