Shift key damaged how to disable it at boot?
You could enable a firmware password.  When a firmware (EFI) password is active it prevents modifier keys during the boot process unless you first disable the firmware password.  Apple's KB article detailing this behavior - HT1352

I'm going to assume that you can't boot to your recovery partition, or an installer disc, thanks to the stuck shift key.  Typically you would enable the firmware password from either of these options, however it's still possible to do from the OS.

To enable the firmware password while inside your OS, 10.7 or newer:


Enter the following string in Terminal.  This enables the debug menu in Disk Utility. defaults write com.apple.DiskUtility DUDebugMenuEnabled 1
Open Disk Utility and choose "Show every partition" from the Debug menu.
Your Recovery partition should now be visible on the left side of Disk Utility, select and click Mount to mount it in your system.
In Terminal, enter the copy &amp; paste the following command to load the Recovery disk image. open /Volumes/Recovery\ HD/com.apple.recovery.boot/BaseSystem.dmg
The Recovery disk should open in a new window, browse to it's /Applications/Utilities folder.
Locate the Firmware Password application and double click to launch it.
Follow the on-screen instructions to enable a firmware password.  I would recommend keeping this password very simple and easy for you to remember.  The firmware password CAN be bypassed but the difficulty of doing so varies between Macs.


If your version of Mac OS X is 10.6 or older:


While booted to your OS, insert the gray restore disc labeled "Install Mac OS X".
Open Terminal and copy &amp; paste the following command, this will open a window showing the Utilities folder from the system installer. open /Volumes/Mac\ OS\ X\ Install\ DVD/Applications/Utilities
Double click the Firmware Password application to launch it.
Follow the on-screen instructions to enable a firmware password.