Is there a way to undo Mocha stubbing of any_instance in Test::Unit

As it happens, Mocha 0.10.0 allows unstubbing on any_instance().

str = "Not Stubbed!"
String.any_instance.stubs(:to_s).returns("Stubbed!")
puts str.to_s   # "Stubbed!"
String.any_instance.unstub(:to_s)
puts str.to_s   # "Not Stubbed!"