I've pulled off something similar by cloning a stereo guitar track and placing an instance of Voxengo MSED on each to essentially split out Mid and Side into separate tracks, allowing each to be effected independently. It was a one-time experiment, though, as I decided it was too much work for too little benefit.
 
But that was before M/S became so ubiquitous. Nowadays I've got compressors and equalizers (Pro-C and Pro-Q in particular) that do M/S and I use them routinely in that mode. And now that lawajava's sparked this conversation, I'm thinking I should explore Timeless2's M/S feature.