Manually Add to DropDownList Populated from Database

Hi

I am using a dropdown list to display a list of values from a database.
Is there a way that I can manually add one item to this list. Basically I want to add a blank entry at the start of the list which is selected by default so that it forces people to actually choose a value from the list. If they don't, it will involk the required field validator.<asp:DropDownList ID="observationFor" runat="server" DataSourceID="teacherDS"
DataTextField="fullname" DataValueField= ...