Not exactly what you're looking for, but many sports fans have discovered if they disconnect the center channel of their surround sound system, they can effectively mute the commentators without muting the rest of the broadcast.
I used to do exactly that to remove lead vocals and guitar lines in songs I wanted to jam with. I think it accomplishes the same thing as stereos with the Karaoke switch. The mono stuff (in dead centre) is removed by switching the +/- on one side and then recombined in the same way to produce the phase cancellation needed for the center alone, left without center, and right without center for Dolby 3Stereo.
There's another (but vaguely related) trick for getting the rear Left and Right channels, and then add a simple low bypass filter for full Dolby 5.1.
If you don't have a center channel in your stereo, but you do have a setting for Stereo Widening, there is another technique: Reverse the phase of one of your speakers by simply plugging in the + and - to their opposites, and then clicking on Expand or Widen or whatever your kit calls it. The middle / mono content will still be there, but only barely.
