Hi!
I am not entirely sure, but it sounds like you want to test the client of the web service.
If that is the case and assuming you are using generated client artifacts of some sort, then
you should have no problem mocking the web service client stub using your favourite mocking framework.
Generated artifacts usually contain a service interface, which I would use to create a mock stub. There are no details in your questions, so I cannot give a more in-depth answer, I am afraid.
Best wishes!