How to add a DropDownList column to GridView?

How can I add a DropDownList column to gridview in code behind? In my case a want to add a dropdown called Employer. I have successfully added 1 string column called Name with the following code:

  DataTable dt = new DataTable();
  DropDownList drp = new DropDownList();

  dt.Columns.Add("Name", typeof(string));
  dt.Columns.Add("Employer", typeof(DropDownList));

  drp.Items.Add(new ListItem("test", "0"));

  foreach (SPListItem item in queryResults)
  {

      dr["Name"] = item["iv3h"].ToString();
      dr["Employer"] = drp;
      dt.Rows.Add(dr);
  }

   BoundField bf = new BoundField();
   bf.DataField = "Name";
   bf.HeaderText = "Name";
   bf.HeaderStyle.HorizontalAlign = HorizontalAlign.Left;
   bf.ItemStyle.HorizontalAlign = HorizontalAlign.Left;
   GridViewEarningLine.Columns.Add(bf);

The Name column is working wonderful but the Employer is showing this message in each row System.Web.UI.WebControls.DropDownList.

I DON'T HAVE ACCESS TO ASPX PAGE SO I CANNOT ADD IT WITH TemplateField