USB Cable Slot

Pieces like that usually go in all one piece units it is possible its just pushed into place without screws.

look for screws on the sides or bottom if nothing is seen try using a tiny straight blade screwdriver to lift it slightly then maybe you can modify it to your needs.

Couldn't you just take a dremel and add a cable slot to the door?

There must be room to drill a hole from the inside out somewhere on the bottom or left side. Then keep that cable always plugged into the usb with glove box closed. Leaving the device plug in always at the ready.