Well, I think the way the ObjectDataSource is intended to be used is you specify the name of the method in your custom business object, and it will use reflection to call that method.
So, your page and object might look something like this:
<asp:objectdatasource
id="ObjectDataSource2"
runat="server"
updatemethod="MyUpdateMethod"
typename="MyBusinessObject">
<updateparameters>
<asp:controlparameter name="anID" controlid="DropDownList1" propertyname="SelectedValue" />
</updateparameters>
</asp:objectdatasource>
Public Class MyBusinessObject
Public Shared Sub MyUpdateMethod(anID As String)
'data access code
End Sub
End Class
This pattern of putting control together can be quite productive, but you'll probably feel too restricted after a while.