What do you mean by "hard wired". I have a non portable GPS in my xB. It is a Garmin G-510 that plugs directly into my Kenwood DDX-6019 and displays its functions on the headunit's screen....I love it. The only visable part is is the small 1.25x1x3/8" antenna ( mounted it on the right rear corner of the roof and routed the lead in thru the rubber factory wire cover at that spot).
I just installed a Pioneer D3 in my xB. It works great! Too many features to list! The only additional part that you will need is the small filler pieces that take up the space between the end of the GPS and the outer frame. The part is available from Crutchfield. Next project - Rear View Camera, 6 Disk CD player and a PAC Steering wheel audio control.