I'm interested to do an led upgrade to my screen too.
In regards to the two way mirror idea, I dont think that would work. Simply reflecting back the incoming sunlight is not good enough...you need to diffuse that light, or else you might just be seeing reflections on your screen. Maybe a sheet of 3M's ESR behind the diffuser panel in your LCD would work.
As for the LEDs, you can get small SMD leds from china on ebay very cheap. Like a bag of 100 of these for a very reasonable price. Quality wise I think they would be ok, but not sure if their brightness specs are realistic or not. I would just take out the ccfl tube and try to fit in as many leds as you can. Although a single led is bright, the light is very focused and not very diffused, so you might need to overdo it a bit. For a typical 7 inch screen, I think you can fit about 30 of these on the width of the screen.
I'd love to see pics if you decide to go with this.