Mock using rihno Mock test

i have a plugin which has RetrieveMultipleResponse as response. 

and now i want to generate stub for RetrieveMultipleResponse class but rihno mock throws error saying you cannot mock sealed class? 

RetrieveMultipleResponse response = MockRepository.GenerateMock<RetrieveMultipleResponse>();
RetrieveMultipleResponse response1 = MockRepository.GenerateStub<RetrieveMultipleResponse>();

both lines throws error. 

Thanks in advance