I'd be perfectly satisfied if I could hide the wires completely. But that means popping the dash, something I've never done before on any car.
Most pieces of the dash just unsnap; if there's any screws, they are usually obvious. I've taken mine apart a few times to route wires for the trailer brake controller, CB, radar detector and, soon, GPS. I'll try to post some pictures later today.
For '07-up Pathfinders, (possibly earlier), you can buy an OEM kit from Nissan that will hold a Garmin 700-series GPS and replaces the dash tray/cover. The GPS snaps into a built-in holder, which is wired directly to the radio wiring harness for power, and there's a lid so the hole thing closes and hides your GPS from sight.
I just picked-up a Garmin 760 yesterday from Best Buy for $349, and ordered the Portable Nav Holder, part number 999q5-ku001, from a local Nissan dealer for $110. Again, I'll post pictures, or you can look at a similar install documented here:
http://www.thenewx.org/phpbb2/viewtopic.php?t=8061