Trying to insert an extra item in a combo box

I populate a combo box on my form using a dataset. I one to add one extra item to the combo box after its populated but every time I try to do that I get an error saying "Items collection cannot be modified when the DataSource property is set.".

Here is how I populate my combo box

SqlParameter[] aryParms = new SqlParameter[5];
                  string strProc = "";
                  DataSet rsMP = null;
                  ExecQuery MPClass = null;

                  MPClass = new ExecQuery();

                  strProc = "vehicle.dbo.spr_get_mkt_program2";

                  aryParms = new SqlParameter[4];
                  aryParms[0] = put some value here
                  aryParms[1] =  put some value here
                  aryParms[2] = put some value here
                  aryParms[3] = put some value here
                  try
                  {
                        rsMP = DesktopDataMeister.ExecuteDataset(DesktopConfigurator.EDBServer, CommandType.StoredProcedure, "vehicle.dbo.spr_get_mkt_program2", aryParms);
                        if (rsMP.Tables.Count > 0)
                        {
                              cboMP.DataSource = rsMP.Tables[0];
                              cboMP.DisplayMember = "marketing_program";
                              cboMP.ValueMember = "program_id";
                        }
                  }

// this is the code I try to insert one more item in the combo box and here is where I get the error.

cboMP.Items.Insert(0, "Please Select a Family Brand...")

cboMP.SelectedIndex = 0



Can you please tell me how to fix this.

Thank you