You can use your laptop to play MIDI files on the Clavinova; you need
a USB to MIDI interface (Yamaha used to do a simple one called the UX16)
and some kind of MIDI player.  VanBasco is a popular shareware package
which should do the trick:

  http://www.brothersoft.com/vanbasco.s-midi-player-11242.html 

Adrian Thomas