[xfire] How to return a mixed array?

Question

Hi all, I'm working on XFire (on Grails) to expose a simple web service. The GaUser class has several subclasses (e.g. employee, admin, etc). The problem is that from this service, I only get the GaUser object, without the fields in the subclass.

GaUser findUserByUserId( String userId ){ 
        GaUser user = GaUser.findByUserId( userId ) 
        // at this point the user is an instance of subclass
        return user 
        // only the superclass is returned to the SOAP client.
} 

In Grails I can't use the 'def' type, so the objects are all cast to the superclass. Any hints? Is there a way to make this work in a more dynamic way?

Cheers!