You can turn it off completely with a KUAL script (not written yet AFAIK). I was turning off the LED from root shell over SSH on my PW1 back before I lost it on a trip. I have a functional PW3 now, so I can explore making such a KUAL extension...
Hmm... I just realized I can probably modulate (baseband AM, or at least PWM) the backlight for audio output for my kindle video player. A photocell connected to amplified speakers should work for that. I may need to build a kernel module for such add-on audio support for mute kindles like the paperwhite (or K4 with modulated power LED) models.
