And to avoid the obvious: "Well if you can add widgets to the lock screen what's to stop people from accessing things that you don't want them to without them having to unlock your phone?"
Just have a menu in the options to allow/disallow specific apps/widgets, and then they won't show up on the lock screen add menu as something that's available.
For example, I personally wouldn't want someone to be able to go into my texts without having my permission to unlock my phone, but something like a camera or the weather or a shortcut to a game even could be cool.