This is how they animated King Kong in 1933. Various matte paintings or miniatures were placed on a small table. The back of the table had a a backdrop (essentially), on which was painted more elements.
The stop-motion puppets would be placed between two of these mattes.
Rear-projection was used to add the element of live-action in a small section of the image. As each frame of stop-motion was filmed, the rear-projection image was moved forward a frame as well.