hmmmm, sounds like another MUMPS/Intersystems Cache developer ;)
Seriously though, you might want to check if there are any tools for 'X' which could map the flow of the program, or as part of the documentation process break out something like Visio or another similar tool where you can walk through the code and map out what it does (more or less). Hardest part would probably be having to go back and stare at that wall of code and jump right back in so anything you can do to document it/graph it/chart it will help.
