What I've done is use CDWav to chop the track into three sections:
#1: the start of the track until just before (i.e., a few seconds, at most) the offending section
#2: the end of section #1 until just after (i.e., a few seconds, at most) the offending section
#3: the end of section #2 until the end of the track.
I then take section #2 and do a complete channel-over-channel copy (using Audacity), making it monophonic. After this, I use WavMerge to put it between the untouched sections #1 and #3, making one big track, with the middle part of it now being monophonic.
Aloha,
Brad