the leds themselves wont be a problem I think, afterall all leds are is miniature lamps!
so all you need to do is run a wire from your brake lights to the spot you want to install the leds.
only problem (a small one tough) is to figure out what resistor you will need. I think you know leds are low voltage thingies so conecting them straight to 12 volts would make them burn out instantly
if hooked up in serie you can get to 12 volts whitout a resistor (similar to some christmas tree lights working on 110 but the lamps are only 6 volt.
ask the salesman about it, I'm sure he can help ya.