There are a couple of threads that show how to do that,
I am doing mine, although work has been keeping me busy as well as just back from NASSIR6.
I bought some spools of leds on ebay (red). I removed the reflector from the bike, heated up the back edges with a hairdryer and very carefully pryed the two apart.
cleaned out as much of the goo as I could. I cut a thin piece of aluminum to fit behind the lens, the LEDs are self stick onto the aluminum. Found out the hard way that the LEDs won't fit behind the square insert section. Then used silicone to glue the parts back together, and furniture clamps to hold it all together. I still need to hook up the wires. The trip to NASSIR6 took priority.
I plan on doing the same to the reflector in the rear fender center. and turn it into a third brake light. Then will probably will do the same thing to the trunk reflectors as well.