I did it on mine when installed the Vielside bodykit replacing the trunk spoiler by another one without the third brake light. I have bought a lid light of about a feet lenght and install it inside with some both side sticking strip on rear glass internal side located on top middle using extended wires to plug it there. The only worst issue is when you applied the brake, it glares red on the rear glass making rear visibility more difficult on the night when you back-up car to park it.
Can take a picture of my installation if you want an idea of it