That picture is EXACTLY what I was contemplating doing with a couple of planes.

The small slot to give it needed clearance... Excellent.

I also see that Hobby Lobby has some Graupner Elevator horns that mount at the very end of the control surface.



The second from the right in the above image.
I may order some to see if they also will work.... though cutting existing horns as you've indicated would be just as effective.

Thanks.