Yes they do make non-integrated tail lights. The search function is great.
on the other hand, you can just use a 2357 instead of a 1157. Brighter brake light filament. No mofication. And it only costs $3 for a pack.
You can also get one of these to put on top or bottom of your plate:
http://www.aerostich.com/stopper-led...t-stopper.html