You can get a little bluetooth radio module that you simply stuff in behind the existing tape deck cd player thing. It just plugs into the main head unit, and you can control previous/next tracks just like a CD, from either the control switches or your phone. Oh, and you can control the volume from your phone too, but I use the control knob (easier). Not sure on your hifi, but you might need to unplug the CD module and plug in the bluetooth thing. They're pretty good actually. Don't go for the cheapest, as they hiss and distort.
800 miles on day 1. OMG! From where to where? We need Lupo GTI pics with some amazing scenery (or cool street signs).