Why on earth is that fixed?? v odd. Does it have features that a portable one doesn't?
Is it just that wire preventing you from taking it out the car? If so you could find out what cables are in there, cut it and solder some plugs on.
Tbh if it were me, I'd remove it completely, sell it on the bay and then buy a normal portable sat nav.
Alternatively, move to a nicer area ;-)