GridViewのヘッダに動的にボタンを追加した後のイベントについて

Dim button As New Button
button.Text = "変更"
button.CommandName = "BtnUpdate"
Me.GridView1.HeaderRow.Cells(0).Controls.Add(button)

↓※イベントに入りません。
Protected Sub GridView1_RowCommand(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewCommandEventArgs) Handles GridView1.RowCommand
    If e.CommandName = "BtnUpdate" Then

    End If
End Sub

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Dim table As DataTable = New DataTable("TestTable")
        Dim column As DataColumn
        column = New DataColumn()
        column.DataType = System.Type.GetType("System.String")
        column.ColumnName = "列1"
        column.Caption = "列1"
        column.ReadOnly = False
        table.Columns.Add(column)

        column = New DataColumn()
        column.DataType = System.Type.GetType("System.String")
        column.ColumnName = "列2"
        column.Caption = "列2"
        column.ReadOnly = False
        table.Columns.Add(column)
        '列を追加する
        Dim row As DataRow
        For i As Integer = 0 To 10
            row = table.NewRow()
            row("列1") = i
            row("列2") = i
            table.Rows.Add(row)
        Next
        Me.GridView1.DataSource = table
        Me.GridView1.DataBind()
        AddHandler GridView1.RowCommand, AddressOf CustomersGridView_RowCommand
        'AddHandler GridView1.RowCreated, AddressOf CustomersGridView_RowCreated
        'ヘッダにボタンを追加する
        Dim addColumn As New Button
        addColumn.CommandName = "Add1"
        addColumn.Text = "ボタン"
        Me.GridView1.HeaderRow.Cells(0).Controls.Add(addColumn)
        Dim addcolumn1 As New Button
        addcolumn1.CommandName = "Add2"
        addcolumn1.Text = "ボタン"
        Me.GridView1.HeaderRow.Cells(1).Controls.Add(addcolumn1)
    End Sub
    Sub CustomersGridView_RowCommand(ByVal sender As Object, ByVal e As GridViewCommandEventArgs)
        If e.CommandName = "Add1" Then
        End If
        If e.CommandName = "Add2" Then
        End If
    End Sub