Forms Data Controls :: RadioButtonList Inside A FormView?

In the website I'm building, I have a form that allows new users to register. Part of this page has mandatory address fields, and I use a postcode lookup field which returns a SuburbID and FullSuburbName (Suburb, State & PostCode) to a RadioButtonList inside an UpdatePanel.

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I then handle the insert process in codebehind, and all this works perfectly on my New Account page.What I'm trying to do now, however, is replicate this functionality in the Edit Template of a FormView on my Manage Account page. The idea being that the user can view their current details in the ReadOnly view, then switch to Edit view to change their address (amongst other details of course). When the FormView changes to Edit mode, it should display the user's current PostCode in the textbox, and the RadioButtonList should display the available Suburbs for that PostCode, with the user's current SuburbID as the initial SelectedValue. If the user changes the PostCode and hits search, this refreshes the RadioButtonList with the new list of Suburbs, and once they have selected a new SuburbID this should get written back to the DB with the rest of the form (when they click Save I mean), using the SQL Data Source Update element. However, I simply cannot get this to work inside the FormView Edit Template and

So far, I have tried to handle the FormView's ItemCreated event and populate the RadioButtonList with the Suburbs that match the user's current PostCode, but if I do this with SelectedValue='<%# Bind("SuburbID") %>' in the RadioButtonList, I get the error "Databinding methods such as Eval(), XPath(), and Bind() can only be used in the context of a databound control."If I then change it to have the SelectedValue populate from the codebehind, this works on the initial switch to Edit mode, but when the user changes the PostCode and hits search, I get a different error "'rblSuburb' has a SelectedValue which is invalid because it does not exist in the list of items."My thinking was that rather than binding the RadioButtonList I would just add the new SelectedValue in the SQLDataSource_Updating method, but it doesn't seem to like that either.