How to use different Storyboards for Full Screen / Split Screen / Slide Over in iOS 9?

Hi,

I am preparing my existing app for iOS 9. The app targets both iPhone and iPad and uses two different Storyboards for the two devices. The iPhone Storyboard uses a

UITabBarController

as root while the iPad Storyboards uses an

UISplitViewController

as root to work as Master-Detail view.

The SplitView is not designed to work with the new Split Screen and Slide Over functions in iOS 9. Actually the existing iPhone layout would work great in these cases. But how do I tell Xcode / my app to switch from the iPad Storyboard to the iPhone Storyboard when ever SplitScreen or Slide Over are activated?

Of course I know about

Size Classes

but as far as I know this only allows my to adapt the size and the position of views but to work with completely different views (like a SplitView in one case and a TabBar in another). The SplitView and the TabBar are the biggest difference between the two storyboards, but not the only one. There are other difference like a slightly different user flow, etc. These things cannot be distinguished using Size Classes, can they?

So, how to solve this?

Do I have to check the current screen size/state in code and load the correct Storyboard manually or is there any way to do this automaticly?