使用App委托访问通过故事板创建的视图控制器

I'm working on an iOS5 app using storyboard, and I have a method in a view controller class that i'd like to access from the App Delegate. The trouble is, this view controller gets instantiated via a tab bar controller in storyboard, so the App Delegate has no direct way of calling the method I want...I'm working on an iOS5 app using storyboard, an