Cloning and extending class in Groovy

I'm trying to generate classes dynamically in Groovy. My approach is this:

class MetaClassTest {

    static class TestClass {

        String getName() {
            return "Jake"
        }
    }

    public static void main(String[] args) {
        def testClass = TestClass
        def metaMethod = testClass.metaClass.getMetaMethod('getName', [] as Class[])
        testClass.metaClass.getName = {
            metaMethod.invoke(delegate) + " and the Fatman"
        }
        assert testClass.newInstance().name == "Jake and the Fatman"
    }
}

This however changes the behavior of the original class which is what I don't want. So my question is:

How can I clone (and probably rename) an existing class dynamically so that I'd be able to create multiple derivates?