[KLF] SFQ

I know this sounds stupid, but does anyone know how B&J (or whoever) manage to extract just the vocals from a certain track. Of course, it'd be easy if there's an accapella version of the track available but, for example, Wanda Dee's "To The Bone" is chock full of goodies used by The KLF, only there's a backing beat running along behind them. Chris