The stump feeder seems like a great idea. I'm in the process of building "my version" of one. I have not seen a "real one" but I have a couple of ideas on how I'd like it to work for me. This first edition will feed with only one outlet and be gravity fed. A second version will contain a Pennco feeder inside the stump. This will regulate the feeding times, by feeding only in the mornings and afternoons. I want to target feeding times to my hunting times.
Of course, this project starts with some chicken wire. Pick a height and diameter that suite you.
Form up some "roots" for authenticity. Add a couple of "access holes" (left arm is through one) around the center cylinder. This will help give you access to the inside, so you can apply the fiberglass internal baffle (that the corn slides down).
Completed skeleton. Wire internal baffle hard to see.