Are you talking about replacing the bulb in the top rear brake light by the window? If so, I think you can get to it from in the trunk. Just get in the trunk and lay on your back and look up. You should see a little cover held in with two black fasteners. Remove those two fasteners and you should be able to get to the bulbs.
If you are talking about the big rear brake light that goes across the rear of the car, you can also get to those from in the trunk. Just remove the plastic trim and pull back the carpet a little and you should be able to change those pretty easy.
1998 Supercharged Riviera - Custom CAI, Alpine spx-13ref, Infinity 6x9's, Alpine 4 Channel Amp, Kicker KX3, Silverstars, STB, Hawk Brake Pads, Monroe Air Shocks, KYB GR2