May I suggest a holster of some sort then, as they really do cut down on this sort of thing....??? On my 7100i and on my previous 7520 and 7510, a locked keyboard is just that--locked--none of the buttons worked at all, other than the scrollwheel to unlock the device....
If your bb is getting unlocked while in your pocket, you've got a whole other set of issues to deal with, and I'd seek out a forum dedicated to that!! LOL