User Interaction on parent UIViewController after Custom Transition

I'm trying to implement the custom transition between two UIViewControllers that was introduced in iOS7. What I'm trying to do is present a UIViewController partially like so:

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There is a parent UIViewController and I'm presenting a modal like animation but which is only 3/4th the screen.

My issue is that I want the button of the previous UIViewController (the blue Button) interactable. Is this possible using custom animations or should I implement the same using containers?

Thanks.