Posting "help me!!!" does nothing. I see all posts that I haven't answered, and do it in order when I do my daily support run.
To do what you're trying to do, you need to write your own logic. UICenterOnChild centers on a child, as simple as that. If you want there to be code that prevents going to the last child, and instead diverts to the second last, then modify UICenterOnChild/UICenterOnClick script to do just that.
NGUI's source code is yours to modify for a reason.
