Adding audio channel to finished DVD

Hi all,

Here is my situation, I have recorded old home videos from tape to DVD.
These DVD's contain multiple short videos (not chapters) and include a menu to select these videos.
During the recording something went wrong and only one audio channel got recorded, when you play the DVD's now only one speaker works in stereo mode.

Is there any way for me to duplicate the single audio channel on these DVD's so that it will sound sort of as stereo without losing the chapter menu and order of the clips?

If anyone could give me any tips that's much appreciated! I'd rather not go through the process of making the menu and everything for all the DVD's all over again...

Thanks in advance. :D

Fabian