Combining Vertex-Fragment and Surface shaders

I don't see many answers to shader questions ere but thought I'd ask anyways. I have a working Vertex Fragment shader that allows 2 textures for the front and back of a mesh(Quad).

The problem is that it doesn't react to lighting. I have another very simple Surface shader that reacts to diffuse lighting. So how do I combine the 2?

In my Vertex Fragment shader I am using the VFACE semantic as an additional argument in my Fragment or Pixel shader function to check which side is currently facing the camera.