You can paint the insides of any ERA/SPF bent steel taillight recepticals with white spray paint and that will improve their reflectiveness/brightness outward toward the red lens.
Also be careful on LED selection...they generate more heat and can melt the lense if too close to it. Not all LEDs that are built for the 1156/1157 socket are alike.
Third, what Tony said...the WHOLE CAR is a brake light. I've managed to cause two accidents so far as a result of rubber neckers. Three more and I'm an ace.
-Dean