Assembly a = [Assembly нужной сборки];
         string rname = string.Format("{0}.{1}", a.GetName(false).Name, "Report1.rdlc");         
         var stream = a.GetManifestResourceStream(rname);

         this.ReportViewer1.LocalReport.LoadReportDefinition(stream);

      public static void LoadReportDefinition(LocalReport report, string reportName)
      {
         var goodsTable = DataHelper.GetGoodsTable(); //Получаем данные
         var a = typeof(ReportHelper).Assembly;
         string rname = string.Format("{0}.{1}.rdlc", a.GetName(false).Name, reportName);
         var stream = a.GetManifestResourceStream(rname);                  
         report.DataSources.Add(new ReportDataSource("DataSet1", goodsTable));
         report.LoadReportDefinition(stream);         
      }

      public static void PrepareReport(LocalReport report, string reportName)
      {
         var a = typeof(ReportHelper).Assembly;
         string rname = string.Format("{0}.{1}.rdlc", a.GetName(false).Name, reportName);
         var stream = a.GetManifestResourceStream(rname);                           
         report.DataSources.Add(new ReportDataSource("DataSet1", new DataTable("DUMMY"))); //Пустая таблица
         report.LoadReportDefinition(stream);         
      }
      ........


      void ReportViewer1_Init(object sender, EventArgs e)
      {
         if (!IsPostBack)
         {
            ReportLibrary.ReportHelper.PrepareReport(this.ReportViewer1.LocalReport, "Report1");
         }
      }
               
      void ReportViewer1_PreRender(object sender, EventArgs e)
      {
         if (IsPostBack)
         {
            var ds = this.ReportViewer1.LocalReport.DataSources[0];
            if (((System.Data.DataTable)ds.Value).TableName == "DUMMY") // Если данные ещё не получали, получим
            {  
               this.ReportViewer1.LocalReport.DataSources[0].Value = WebService.Data.DataHelper.GetGoodsTable();
            }
         } 
      }

      void ReportViewer1_ReportRefresh(object sender, System.ComponentModel.CancelEventArgs e)
      {
         if (IsPostBack)
         {
            ReportLibrary.ReportHelper.PrepareReport(this.ReportViewer1.LocalReport, "Report1");
            this.ReportViewer1.LocalReport.DataSources[0].Value = WebService.Data.DataHelper.GetGoodsTable();
         }
      }