It is very simple to poke the wire behind the headlining and pillar trim. I did not need to take any trim off or unclip it. Just be sure your hands are clean, and the cable of course, you don't want marks on the trim pieces.
The easiest and safest wiring method is to use the built in 12v socket. It is fused and ignition controlled, which is ideal unless you want to use a "park cam" which monitors the car when parked, then you need permanent power.
My camera only operates with the ignition on, which suits me.