I recently came across this article which has a technique for removing a hook from the gullet. I had a chance to try it last night on a deeply hooked flathead, and it worked quite well. A similar article in the In-Fisherman magazine (Feb 2005) stated cutting the line should be a last resort.
For catfish, the only thing I would recommend, is a long needlenose pliers. My Leatherman worked for me last night, but was a little on the small side. Good luck!