This is a remix of the best Fire HD tablet mount.
Changes:
There are two options. One uses the original idea of passing the USB cable through the bottom of the mount to run down the wall. The second option has a trench to route the cable out the back.
If needed, the pin holes are 4mm or 5/32" on the inside and 3mm or 1/8" on the outside. Worst case (if your holes still come out a little narrow) a few turns with the right drill bit size by hand should be enough to get the clearance right for the pins.
I use these cables as they're cheap, work well, and have the 90° connector. For my in-wall cables, I'm using these power supplies in the bottom outlet to keep the cable as out-of-sight as possible. I drilled a hole behind the tablet big enough for the USB A side of the cable to fit into the wall. Using a magnet, I pull the connector back out next to the electrical box. A small notch on the bottom of the faceplate lets you put the cover back on with the cable routed out the bottom.