Add custom column while exporting Excel from GridView in ASP.Net

I am able to save excel sheet from GridView perfectly. However, I need to add one custom column, which will be URL of a file on sever, I am not allowed to add URLs directly in the table (as per company's development policies). What is the best way to achieve this? I tried pulling URL from web.config however I am not sure where to add that in the following code

<asp:GridView ID="bestpractgrv" runat="server" AutoGenerateColumns="False" CellPadding="3" GridLines="Vertical" Width="100%" BackColor="White" BorderColor="#999999" BorderStyle="None" BorderWidth="1px" PageSize="10" AllowPaging="True" OnPageIndexChanging="OnPaging" DataKeyNames="iID">
                <AlternatingRowStyle BackColor="Gainsboro" />
                <Columns>

                <asp:TemplateField>
                    <HeaderTemplate>
                        <asp:CheckBox ID="chkboxSelectAll" runat="server" onclick="CheckAllEmp(this);" />
                    </HeaderTemplate>
                    <ItemTemplate>
                        <asp:CheckBox ID="chkSelect" runat="server" />
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:TemplateField HeaderText="Discipline" Visible="false">
                    <ItemTemplate>
                        <asp:Label ID="iid" runat="server" Text='<%# Bind("ID")%>'></asp:Label>
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:TemplateField HeaderText="Discipline">
                    <ItemTemplate>
                        <asp:Label ID="discplnlbl" runat="server" Text='<%# Bind("cDiscipline")%>'></asp:Label>
                    </ItemTemplate>
                </asp:TemplateField>

VB CODE

Private Sub ExportFunction()

        SaveCheckedValues()
        Response.Clear()
        Response.Buffer = True
        Response.Charset = ""
        Response.ContentType = ContentType

        Dim sw As New StringWriter()
        Dim hw As New HtmlTextWriter(sw)

        bestpractgrv.AllowPaging = True
        BindDataGrid()
        bestpractgrv.HeaderRow.Style.Add("background-color", "#FFFFFF")
        bestpractgrv.HeaderRow.Cells(0).Visible = False

        For i As Integer = 0 To bestpractgrv.HeaderRow.Cells.Count - 1

            bestpractgrv.HeaderRow.Cells(i).Style.Add("background-color", "#df5015")
            bestpractgrv.HeaderRow.Cells(i).Style.Add("color", "#FFFFFF")

        Next

        If ViewState("CHECKED_ITEMS") IsNot Nothing Then

            Dim CheckBoxArray As ArrayList = DirectCast(ViewState("CHECKED_ITEMS"), ArrayList)
            Dim rowIdx As Integer = 0
            'Dim pdfloc As String
            For i As Integer = 0 To bestpractgrv.Rows.Count - 1

                Dim row As GridViewRow = bestpractgrv.Rows(i)

                row.Visible = False

                Dim index As Integer = CInt(bestpractgrv.DataKeys(row.RowIndex).Value)


                If CheckBoxArray.Contains(index) Then

                    row.Visible = True
                    row.Cells(0).Visible = False


                End If

            Next

        End If

        bestpractgrv.RenderControl(hw)

        Dim rgrvw As String
        Dim idate As Date = DateAndTime.Now
        Dim filedate As String
        Dim fileloc As String
        Dim fpath As String
        Dim filename As String
        Dim htparam As New Hashtable
        Dim mode As String = "insert"


        'fpath = "C:\excelbooks\"
        fpath = Server.MapPath("~/Excelbooks/")


        filename = "bestpractices"
        filedate = idate.Month & idate.Day & idate.Hour & idate.Millisecond
        rgrvw = sw.ToString()
        fileloc = fpath + filename + filedate + ".xls"

        System.IO.File.WriteAllText(fileloc, rgrvw) '<-- excel file is generated and copied in specified folder

        htparam.Add("@date", idate)
        htparam.Add("@location", fileloc)
        htparam.Add("@mode", mode)

        Dim ds As New DataSet

        ds = Customdll.Functions.AppExecuteSelectDataset(CommandType.StoredProcedure, "STORED_PROCEDURE", , htparam)

    End Sub