Contact in a child of User, so Contact can exist without an User. This means that every time you create a Contact, a User is created as well. The same is for Person parent.
What you can do is add another Contact entity to your LLBLGen project (Contact2, for instance). Such entity doesn't inherit from User, just reference it. That way you can create a Contact which will create only a contact row in db:
Contact2Entity myContact = new Contact2Entity();
myContact.User = theUser;