I have successfully installed a blackvue 650 dual channel dashcam without hardwiring it.
All the cables are hidden.
There are no visible cables except for the plug which is plugged into the 12v socket in the trunk and not in the front dashboard.
I didn't want to hard wire anything into the car but I also didn't want to plug it into the dash, I think the plug in the trunk is a great alternative.
Also, keep in mind that the pillar behind the rearview mirrior is huge on this car so I mounted the camera to the left of the pillar on the drivers side and not the passenger side.
I also mounted the rear camera on the drivers side on the bottom of the glass.
I did that for the following reasons.
1) if you top mount it, the top wing/lip on the hatch will obstruct the view.
2) if you mount it in the bottom center, the wiper will not clean that area. There will be a half circle of dirt.
3) if you mount it on the bottom passenger side, the wiper rests there and will block the view
The only suitable position I found was bottom of glass on the drivers side. The wiper clears this area also.
Power cable was routed starting from the back of the car and going along the passenger side.
Channel 2 cable was routed starting from the front of the car and going along the drivers side.
Let me know if you have any questions. I will post the footage and some photos soon.