Need urgent help integrating a Unity 5 + Vuforia 6 project into a native iOS App

We have created a project with Unity 5.3.5 and Vuforia 6.0.114 and need to integrate it into a native iOS App with a Storyboard based UI. We are familiar with the process of integrating a Unity App into a native iOS App itself and we made everything work fine as long as there is no Vuforia involved.

The problem is that Vuforia itself subclasses Unity's Controller (in VuforiaNativeRendererController.mm) by using the IMPL_APP_CONTROLLER_SUBCLASS(VuforiaNativeRendererController) mechanism.

This is actually the same way we subclass our own iOS native App, thus we have a conflict. We can either start our part and take control of Unity or let Vuforia do it.

The question now is: Is it possible to somehow further subclass Vuforia or something similar? And if so, how could this be achieved?

We are searching all kinds of forums and blogs, but we can't find a working solution. Since this is really urgent, we would be glad for any helpful respond. Or maybe someone knows where to find a working tutorial?

Thanks in advance!