Luke, I know you're trying to stick to original stuff but since you're considering a third brake lamp for safety reasons this might also be of interest. ...I assume you are using glass lenses on your tail lights... you might consider switching to the 21cp bulbs, if you haven't already, and the repop plastic lenses. I found the plastic lenses allow significantly more light to pass through and when paired with the 21cp bulbs are more than adequate for day and night driving. Plus they'll look more original than a third brake lamp.
Just a thought.
Here's a comparison of the two...
http://www.flickr.com/photos/ericdifate/6321986157/
