The invisicord is an easy way to do it....it will plug right into the back of the mirror.
I have an older V1 that is hardwired using their flat cord. Run the cable along the headliner to the passenger side. If you remove the grab handle on the a-pillar, you can work the trim far enough back to run the wire down to the top of the dash. If you remove the trim panel on the right side of the dash adjacent to the door, you will see a bolt (which can be used for a ground) and some wiring (which can be tapped into.) I'll have to look tonight to see what color I tapped into, but if memory serves me, it was yellow and gray. Connect the "+" lead to this wire and your detector will power up with the key on.
I'll take some pics and post them later today.