After rereading your post we are not really sure what you are trying to accomplish.
By default "Unexpected calls" (i.e. calls that have no expectation set on them) are executed by the "real" code. the exception for this rule are interfaces/abstract classes which has no "real" code and calling unexpected methods will end in an exception thrown.
So, if I understand you correctly the behavior you need should be the one you see by default.
Since this is not what you see, try using the StrictFlags Enumeration as Paulo suggested and if still thing does not work for you, try posting you test code and as much of the code under test as you can.