--- src/ooxml/java/org/apache/poi/xssf/streaming/SXSSFSheet.java	2015-01-17 17:58:04.361835949 +0200
+++ src/ooxml/java/org/apache/poi/xssf/streaming/SXSSFSheet.java	2015-01-19 10:08:10.993864745 +0200
@@ -1140,6 +1138,34 @@ 
                 ct.addNewSheetFormatPr();
         if(outlineLevelRow > 0) pr.setOutlineLevelRow((short)outlineLevelRow);
     }
+    
+    /**
+     * Set row groupings (like groupRow) in a stream-friendly manner
+     *
+     * <p>
+     *    groupRows requires all rows in the group to be in the current window.
+     *    This is not always practical.  Instead use setRowOutlineLevel to 
+     *    explicitly set the group level.  Level 1 is the to level group, 
+     *    followed by 2, etc.  It is up to the user to ensure that level 2
+     *    groups are correctly nested under level 1, etc.
+     * </p>
+     *
+     * @param rownum    index of row to update (0-based)
+     * @param level     outline level (> 0)
+     */
+    public void setRowOutlineLevel(int rownum, int level)
+    {
+        SXSSFRow row = _rows.get(new Integer(rownum));
+        row.setOutlineLevel(level);
+        if(level > 0 && level > outlineLevelRow) {
+            outlineLevelRow = level;
+            CTWorksheet ct = _sh.getCTWorksheet();
+            CTSheetFormatPr pr = ct.isSetSheetFormatPr() ?
+                ct.getSheetFormatPr() :
+                ct.addNewSheetFormatPr();
+            pr.setOutlineLevelRow((short)outlineLevelRow);
+        }
+    }
 
     /**
      * Ungroup a range of rows that were previously groupped