If you do not want a field in yor data file then set it sbinding to None. Note that you cannot change the binding programmatically. Once the form is rendered with a set of bindings then you are done. They cannot be changed.
Sorry people for bringing this question forward again... but I'm on a serious deadline (project due tomorrow) and I really need to know if it is possible to customize the XML data file or not. And if yes, how?