ItemCommand event not propogating on ImageButton click

Sorry for the stingy point allocation, it's all I have left!  I have a datagrid with a dynamically generated template column below that contains an ImageButton.  I would like for when the button is clicked, the ItemCommand event is raised on the datagrid.  In the following code, this does not happen.  Is there a way to get this to work?  

Cheers, Steve.

public class DGTempColumn : System.Web.UI.Page
{
      protected System.Web.UI.WebControls.DataGrid DataGrid1;

      private void Page_Load(object sender, System.EventArgs e)
      {
            DataSet ds = new DataSet();
            DataTable dt = new DataTable();
            ds.Tables.Add(dt);
            dt.Columns.Add(new DataColumn("test 1"));
            dt.Columns.Add(new DataColumn("test 2"));

            DataRow dr = dt.NewRow();
            dr["test 1"] = "test 1 1";
            dr["test 2"] = "test 2 1";
            dt.Rows.Add(dr);

            dr = dt.NewRow();
            dr["test 1"] = "test 1 2";
            dr["test 2"] = "test 2 2";
            dt.Rows.Add(dr);

            DataGrid1.DataSource = ds;
            DataGrid1.DataBind();
      }

      private void Handle_DataGrid1ItemCommand(object sender, DataGridCommandEventArgs args)
      {
            string test = args.CommandName;      // NOT HIT
      }

      #region Web Form Designer generated code
      override protected void OnInit(EventArgs e)
      {
            TemplateColumn tmView = new TemplateColumn();
            tmView.HeaderTemplate = new AddColumn(ListItemType.Header, Page);
            tmView.ItemTemplate = new AddColumn(ListItemType.Item, Page);
            DataGrid1.Columns.Add(tmView);

            DataGrid1.ItemCommand += new DataGridCommandEventHandler(Handle_DataGrid1ItemCommand);
            InitializeComponent();
            base.OnInit(e);
      }

      /// <summary>
      /// Required method for Designer support - do not modify
      /// the contents of this method with the code editor.
      /// </summary>
      private void InitializeComponent()
      {    
            this.Load += new System.EventHandler(this.Page_Load);
      }
      #endregion
}

public class AddColumn : ITemplate
{
      private ListItemType templateType;
      private Page parentPage;

      public AddColumn(ListItemType type, Page page)
      {
            templateType = type;
            parentPage = page;
      }

      public void InstantiateIn(System.Web.UI.Control container)
      {
            switch(templateType)
            {
                  case ListItemType.Header:
                        break;
                            case ListItemType.Item:
                        ImageButton imgPlus = new ImageButton();
                        imgPlus.CommandName = "Add";
                        imgPlus.Width = 10;
                        imgPlus.ImageUrl = @"~/images/plus.gif";
                        imgPlus.ToolTip = "Click to add or insert.";
                        container.Controls.Add(imgPlus);
                        break;
            }
      }
}