Customize Event Manager forms-how?

I need to add several form fields to forms generated by an existing module, Event Manager, for its Event registration forms (as distinct from user registration forms). It seems to me that Event Manager deals with forms completely on its own-or I'm just not understanding how to leverage CCK, which would be preferred. In any um, event, what would be the prescribed method for adding several form fields to an existing module that doesn't talk to CCK?