I figured it out. There is a control in the Windows Phone Toolkit that has the exact same behavior I am looking for. The TiltEffect dependency object enforces it's parent type at compile time. "Property IsTiltEnabled does not support values of type ..." I just have to do the same, but for the Children of my control.
What you need to do, more specifically is change the Items (through ItemsSource...) of the ItemsContorl to be a strongly typed collection, e.g. an ObservableCollection