What about having an ancestor class and then a super ancestor class? e.g.

```
class MethodDouble
  class Expectation < MessageExpectation; end
end
class VerifyingMethodDouble < MethodDouble
  class Expectation < Message Expectation;
    #specific stuff
  end
end
```

Although I'm not sure that's any prettier... or setting the class in an initialize to an instance var and overriding initalize instead?