Disabling middle button on direction pad?

Just wondering if anyone knows how to disable the middle button on the directional pad? Every time I try to play a game with it, I end up hitting the button with my thumb and another program opens.
I have read of some who claim to have disabled it yet I cannot figure out where to do this. I have looked within under settings/buttons yet it doesn't seem to be listed there; am I missing something? Any help would be appreciated, thanks.

[|oLo|]

get a game pad

[Li0rE]

yea. go to the second tab on button settings

yea. go to the second tab on button settings

Under Settings/Buttons/Up,Down Control, I still do not see an option to change the middle button. The only options I see are: 1) Delay before first repeat and 2) Repeate rate.