+1 to this question.
I have looked for a solution over xda but without success.
Also the intensity of the button backlight is very high which is a little bit unnecessary.
But on the other hand I guess we should be happy that somebody havent programmed these buttons in such way that they lit-up whenever the screen is on
BTW could you point what else do you do with the hard buttons? I can't find them very useful besides answering/ending a call.