Create a factory method on a base class for Jaxb objects?

Question

I have generated some Jaxb objects with the XJC tool. These classes extend one common base class. So for example:

Base.java - Hand-written

@XmlTransient
public class Base {
    public void beforeUnmarshal(Unmarshaller unmarshaller, Object parent) {
        //...
    }

    public void afterUnmarshal(Unmarshaller unmarshaller, Object parent) {
        //...
    }

    //...
}

H1.java - Generated from XJC

@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name = "", propOrder = {
    "content"
})
@XmlRootElement(name = "h1")
public class H1 extends Base {
    //...
}

I want to override the behavior of a handful of these generated classes through a factory method, but I don't want to change the code that's generated from XJC because I want to keep these classes open for other uses, not just my current project. For example, I'd like to extend the H1 class (we'll call it H1Extended) and add a couple attributes, and each time the H1 tag occurs in the XML, Jaxb would return an instance of H1Extended instead of H1.

I tried placing a factoryClass annotation on the base class like this...

@XmlTransient
@XmlType(factoryClass=MyFactoryClass.class, factoryMethod="create")
public class Base {
    //...
}

... but that didn't work. What I would like is a factory method that creates the class generated by XJC by default, and returns a custom class for the ones I specify.

I don't mind re-generating the Jaxb classes with XJC, but I want them to utilize base classes that the programmer will create, and once they're generated, they cannot be hand-edited.

Is this possible? Thanks.

EDIT: I didn't notice the generated ObjectFactory class. Could this be used to accomplish what I'm looking for?

EDIT #2: I extended the ObjectFactory class and overrode one of the create methods to return H1Extended, but the base H1 class is being returned for some reason.

EDIT #3: I'll shorten my question: if I have a JaxB class H1, how do I have the unmarshaller return H1Extended?