I was travelling this weekend. I just got back. No time to work on a serial plug (yet). Soon...
If you have access to a piece of circuit board, you can cut out traces manually with a hobby knife. A knife with a V-shaped blade works the best.
You may have to grind down the circuit board to be thinner to fit in the kindle 3 slot.
As mentioned earlier, I want to figure out a simple way to make a connector from common materials.