That's exactly what I needed to do, but the menu option for that in WebEx Recording Editor 2.8 gave me "invalid wav format". The suggestions in the discussion following the blog post were very helpful. Basically the wav file has to be in CCITU u-law format. The Sound Recorder in Windows XP can make the conversion very easily. Not the one in Vista though, which doesn't seem to allow opening and manipulating an existing wav file.
The tech support from WebEx really shouldn't just say "it's not supported", which probably was the easiest to do. Give the most details they could find and let the users hack their way. Again, it's a rare thing to find a tech support with spirit these days.