As of now, this is not possible unless you parse all the existing faces already present.
I have implemented a new data structure in VTK named vtkStaticFaceHashLinksTemplate, which vtkGeometryFilter uses to get the external faces. I am envisioning that it could also be used for extracting the internal faces of a mesh, along with internal and external together, which is what you need. I don’t know when I will have some time to work on it, but I hope it will be soon.