This is a little and ugly app that allows you to precue tracks from iTunes.
Open the app, choose the output device and volume to use.
Go to iTunes and press CMD + P or drag & drop files in the PreCue window for it to start.
This will not affect the track been played on iTunes. It only works for songs locally stored on your computer.
Together with iTunes built-in Up next playlist you are able to do some DJ-ing.