Adding ListBox Item in a DetailView

I currently have a DetailView that has a TemplateItem that has a ListBox in it. The ListBox is databound to a SqlDataSource. When a User clicks on the Edit of the DetailsView, I want to add an item to the listbox.
here's my HTML:
                                            <asp:TemplateField HeaderStyle-VerticalAlign="Top" HeaderText="Warrant Number(s)">                                                 <EditItemTemplate>            &n ...