How can I disable the Macbook keyboard (from startup)
You can try this to disable the keyboard kext, although I'm not sure if it will work at boot time. Enter this command in Terminal:

sudo kextunload /System/Library/Extensions/AppleUSBTopCase.kext/Contents/PlugIns/AppleUSBTCKeyboard.kext/


To re-enable the keyboard kext, type

sudo kextload /System/Library/Extensions/AppleUSBTopCase.kext/Contents/PlugIns/AppleUSBTCKeyboard.kext/


Source: http://forums.macrumors.com/showthread.php?t=433407

To bypass Safe Boot with a stuck Shift key, hold down alt at startup and select the Mac OS X bootable partition.