Play folder or file in iTunes without adding it into library
http://www.macworld.com/article/1049828/listenonly.html
may be out of date of course ... this link takes you to an article that seemingly explains how to do what the OP requires ...


  Make sure you can see the iTunes window, specifically the Source
  column, along with the song you wish to listen to. Hold down the
  Option key and drag the song file into an empty spot in the Source
  column. iTunes will create a new playlist containing the dragged song,
  but it will not add it to the library. When you’re done listening,
  just delete the playlist. The original file will be untouched, and
  once the playlist entry is gone, iTunes will no longer be aware of the
  song, either.