Not so difficult to find…
Benoit did it for Plane.
http://diydrones.com/forum/topics/how-do-you-use-graupner-sumd-with-pixhawk?commentId=705844%3AComment%3A2336756
http://discuss.ardupilot.org/t/arduplane-3-7-1-graupner-gr-16-receiver-and-sumd-protocol/12606