Any way to tweak it? I'm guessing no, but I wouldn't have ever thought of overclocking a cpu would work either...
I doubt it. You'd have to somehow increase the brightness of the LEDs (or CCFLs) that constitute the backlight, and I doubt simply over-volting them would work. The only way I can think of would be to install more LEDs, but that is non-trivial.
What is the specific situation that requires a brighter screen? Maybe someone here can come up with a different solution that would work. (I tend to have the opposite problem: the screen is often too bright for me, even at the lowest setting.)