Are extras (Nav, CD) an option later?

Hi everyone! I may be somewhat unique on this board in that I'm not yet an owner, but am currently considering buying a used 2001 Prius from Hertz. Because of that alone, I'm somewhat hesitant (how many butts have been in my future command chair?). What really gives me pause, however, is not knowing whether or not I'll be able to add the "cool add-on stuff" later.

I had the pleasure of test driving the Prius in question yesterday. My God, I actually fit into the thing (a rare thing for me). Anyway, I was cruising along and showing my son all of the nifty animations on the touchscreen (Big thanks to John for whetting my appetite and teaching me about this stuff so my son was mystified by my intimate knowledge of the thing). Just for kicks and giggles, I hit the NAV button and the CD button, and in each case it said something to the effect of "external system not connected". Well, I expected them not to work ( knew these weren't included in that particular car), but the thought of "dead buttons on the console" horrified me, so I hoped I could add these items later.

Just to be sure, I called my local Toyota dealer (they do sell Priuses, so I am ASSUMING they are a Prius-authorized dealer), and asked about adding the navigation system and/or cd changer later. The Parts guy to whom I spoke wasn't sure (which again, gave me pause), but said he thought those items had to come included with the car and couldn't be added later. Something about there not being connectors built in to units which weren't pre-equipped with the stuff beforehand.

So the question falls to you, the experts. If I were to buy this used Prius today (or sometime soon), would I be able to add the navigation system and/or CD changer at a later time? My only concern is that I'm an avid gadget freak, and I would HATE to have a bunch of buttons on my console that were dead and destined to do nothing but taunt me for the life of the car. I'm interested only in stuff which will be operable from the dashboard controls; not some helter-skelter auxiliary panel velcroe'd to the dash. Your collective knowledge and experience would be greatly appreciated.