you could break it like i broke mine
all you have to do is pry off the earpiece, there is a ribbon cable that connects the lock/unlock to the mute button (on the other side). if you cut that cable, the button will no longer function.
if you wished to lock/unlock your device in the future, you could do it thru the screen icon. to unlock, hold down the end call button.
.....or look into a case that leaves an opening over the button.