Automating M/S Processing

There are some good threads out there for Mid-Side processing -- for example:
http://forum.cakewalk.com/tm.aspx?m=1729592&high=mid+side+MSED
 
But I would like to activate M/S processing only on selected parts of a song (for example, just on the chorus).
Could this be done with automation envelopes?   With all the extra buses the article above shows, it seems like it could be tedious.
Suggestions on the best way to implement?
- john