Does validation still need the binding?

Question

In Net 3.5 to set a validation rule in WPF you had to set binding as well. Is it still true for Net 4.0?

If yes, is there any easy workaround for that? I.e. setting validation without setting binding.

I am asking because adding regular binded value is an overkill for me (in this particular case) -- I just show a dialog, if user clicked OK, I read values from widgets, if she/he clicked cancel, I do nothing. No binding needed.