2003 prius stock radio upgrade

Hi guys,
First off your site is awesome, So thanks for letting me in on this shindig.

Second I have a pretty base 2003 Toyota Prius. It has the cassette deck and nothing else. I recently bought a stock Toyota Prius Cd player and want to install it. The cd button is there but says no external system installed. The only place the pin from the cd player fits is in the master control which ofcourse won't let me use any controls. The master pin does not use up all the connections which leads me to believe I must figure out what is what and hook it through there. Otherwise I need to hardwire it in I suppose. Is there any actual way to do this? I would rather have a stock Toyota cd player but if there is no way then I guess I am screwed lol. Any help would be greatly appreciated thank you so much