Anyone know how to remove the 3rd brake light in the Avalanche?

I can find videos/instructions all day for the Tahoe/Escalade/Trailblazer, but nothing for the Escalade EXT or Avalanche. Got a new light and want to install it this weekend, but I can't find any instructions on-line, and the new LED light bar didn't come with any.

Please tell me I don't have to pull all the rear interior out to get at it.