You could use the same fuse/ground that I used for my autodimming mirror and PNI compass...
There's an aux fuse in the fuse box under the driver dash and a nice bolt you can use for ground at the base of the dash near the door. (I pulled the fuse, folded wire over one blade and plugged it back in) Do you intend to mount the detector up high by the mirror or down low on the dash? Routing wires along headliner and down the pillar under the rubber trim is cake, tho I'd be careful not to interfere w/ operation of side airbags (if equipped) should they deploy.
I've thought about hardwiring my Passport 8500 too... but for now, it's mounted at dash level just above the center speaker w/ the smartcord in the cig lighter. I had a tint shop install a limo black "eyebrow" along the top of the windshield to make it darker and to hide my compass. Having the detector up there may not be a bad idea...
