I have finally started messing around with creating some apps that work with RESTful web interfaces, however, I am concerned that I am hammering their servers every time I h
You can't. Best thing to do is wrap it in a proxy object, and then mock that. Alternatively, you'd have to use a mock framework that can intercept types that can't be mocked, like TypeMock. But you're talking about bucks, there. Better to do a little wrapping.
Apparently you can with a little extra work. Check the highest voted answer here.