How to disable brightness keys

I have calibrated my display for use with Photoshop. Inadvertently hitting either brightness up or down screws up the calibration (you can't precisely return to the previous brightness setting). Does anyone know if it's possible to disable those two buttons on the keyboard? If so, how?

(I can do it on my G5 through Keyboard Shortcuts but the same capability is not available on my MBP.)

TIA,

KP