can you walk without using your feet?
maybe you're looking for some plugin, but all they do - is shift the pitch.
question two:
yes, utilizing a common karaoke-technique, you've got to filter the mono-signal, as most vocal tracks are put right in the middle of the mix.
adobe audition has a plugin built in, theres the analogx vocal remover plugin, and i'm sure there are some more out there which i don't know of.
also, you can kill the mono-signals by playing around with phase reversing or so... i think you have to copy the track 1:1 into another and then phase-reverse one of them. summin like that.
problem with all those techniques is - killing the mono signals will most definitly cut out drums & bass as well. also, all reverb over the voice that has been spread in stereo will remain.