I'd like to offer my solution to the back button because I think all the other solutions are project specific.
I would not touch the Direct3DInterop Class but change the Cocos2dRenderer::OnBackKeyPress() as follows.
This way It will react the exact same way as android when we overload the virtual void keyBackClicked(void) function in our layers
NB Don't forget to add setKeypadEnabled(true); in the init of your layers.
I'll try and get this merged upstream soon