How to prevent Base Class methods from being called?

My (legacy) MVC application has the following hierarchy of controller classes:

public class CMSController : BaseController
{
        public virtual void SetModelValues(ModelBase model)
        {
            model.CurrentPageURL = Request.Url.ToString();
            // set more model data...
        }

}


public class PageController : CMSController 
{
        public ActionResult Index()
        {
            MyModel model = new MyModel();
            base.SetModelValues(model);
            ViewBag.Title = "My Title";
            return View(model);
        }
}

I am writing unit tests for the PageController.Index method.
I am trying to Fake the call to base.SetModelValues, so that it is not invoked, but can not get this to work.

    var fake = Isolate.Fake.Instance<CMSController>();
    Isolate.Swap.AllInstances<CMSController>().With(fake );
    Isolate.WhenCalled(() => fake.SetModelValues(null)).WillThrow(new Exception("my exception"));

    // Creating an instance of PageController
    PageController _controller = new PageController();

    // Call the index method
    var result = _controller.Index() as ViewResult;

    Assert.IsNotNull(result);

When I run my test however, the actual base.someVirtualMethod still gets invoked.
Can I declare a Fake (or Mock?) in my test which will prevent the real base.someVirtualMethod from running?