As far as I remember, you could see the german voice talent credits in the movie theatre back then (if you stayed long enough to see it and the projectionist didn't make you leave by closing the curtain early).

However these were put there as a reel addition, so those were not included in the home video releases.

EDIT: Just got an idea. What could be done instead of expanding the official credit roll, is some sort of content for the extra disc. A photo of the voice actor with a short bio and filmography of films they voice acted in (or something along those lines).