http://www.aerostich.com/stopper-led...rsa-light.html
You could do one of these on both top and bottom of the license plate. I know it's awfully minimalist, but if you wired some red LED's on the passenger pegs also, you would be mostly legal.
It looks like he did something like that in this picture
http://www.ninjette.org/forums/attac...achmentid=8765
there's one red bar above his plate. I would assume that's his brake light