Needing To Disable Built In Keyboard

Is there a way to do that? My keyboard that was built in just fried out so I bought a new one and have it hooked up via USB. However, the alt button on my built in occasionally goes crazy and is reading like it's being repeatedly pressed.

Is there a way to 100% disable that keyboard???

EDIT: One thing that I did do, and I have no idea if this will work, but I went into System Preferences and went to where you deal with the keyboard and mouse, opened up the modifier keys, and selected just the normal keyboard that I have and no the built in. I doubt that'll do the trick, but I thought I'd add it it.

If it were me I would just take the machine apart and physically disconnect the built in keyboard. There are guides to do this on ifixit MacBook Pro . One thing I cannot predict is the machine may freak out if it doesn't register an internal keyboard, but I would definately give it a shot. It sounds likes your machine is already out of warranty since you didn't mention taking this to an apple store.

Did you finally try if the machine makes any trouble if you disconnect the keyboard from the logicboard?

I am in need of a solution as my built-in keyboard seems to have the SHIFT key constantly pressed (after liquid got into the machine) which results in safeboot all the time. I have an external bluetooth keyboard anyway which works fine once booted but during the boot the SHIFT will create trouble.
I would proceed as in step 15 in the guide:
MacBook Unibody Model A1278 Logic Board Replacement - Page 5 - iFixit

Thanks!

EDIT: I have been roaming the net a bit already for other means of disconnecting the keyboard which doesn't seem too easy but came across this way in the terminal - haven't tried it yet as (i) I wanted to avoid messing in terminal where I am not too much an expert and (ii) it may not help my situation because with reboot it seems this command doesn't apply anymore.
http://forums.macrumors.com/showthread.php?t=433407