Unit test a dynamic instance throws exception if not abstracted from a specific base in c#

I have a class similar to the following

class ObjectCaller
{
    public void Process (String NameSpace) {

        Type t = Type.GetType(NameSpace + ".Main");
        if (t != null)
        {
            if (t.IsSubclassOf(typeof(Window)))
            {
                Object obj = Activator.CreateInstance(t);
            }
            else {
                throw new NotAbstractedException();
            }
        }
        else {
            throw new MainNotFoundException();
        }

    }
}

A namespece is passed to the Render() Method of the class and the passed namespace should have a class .Main and also the class should be abstracted from Window class. Which is working fine. But I am unable to do unit test so that if the class Main exists but it is not an abstract class of Window, it should throw an exception.

    [TestMethod()]
    [ExpectedException(typeof(NotAbstractedException))]
    public void MainNotAbstractedTest() {

        ObjectCaller oc = new ObjectCaller();
        oc.Process("name.space.of.class");
    }

I have tried using MOQ to MOCK System.Type classes IsSubClassOf method and with searching have found that its not possible to MOCK static classes. And also I don't want to change ObjectCaller just for the purpose of UnitTesting, Is there any possible way to make the method Process throw the exception NotAbstractedException without changing the class i am loading dynamically or no changing ObjectCaller ?