I know there was a lot of talk about this when they first came out, but I have been too lazy to look it up (I'm interested in this too.) I'm sure a bit of googling will come up with an answer.
I replaced the red LED in my logitech optical cordless with a 3 volt blue superbright LED. Its not really hard if you've ever used a soldering iron before. This should help.
http://woodstock.uplink.net/~epevel/overview.html