Do you want to do this dynamically while the form is running? I think this will be hard. You can programmatically change a secondary data source that is bound to the dropdown, but you'll have to write code to refresh the view. The dropdown is a windows control which is initialized OnLoad. It doesn't update dynamically and there's no easy way to access it. Why not just use a Web service or database to populate the dropdown?
Patrick Halstead
Project Manager at Qdabra