theres the analog-x plug that removes vocals. results vary, its a bit hit and miss. i always wondered if you couldnt just modify the code on that plug so that it dumps the data it removes in a wav?
EZ Stan the man!!!
Heres a cool video if you ent seen it already (its a good watch even if you don't really want to use the theory anyways) http://www.youtube.com/watch?v=8WNO2aPK3bY
That is the best way of getting a 'pella, i have done it and it really works very well.