Extjs-3.4 Checkbox in specified column of checkbox group

I am using ExtJS-3.4 ,in which I need to show the checkboxgroup with 9 checkboxes and I am able to show the checkboxes in checkboxgroups with two columns. The two column controls(checkboxes) were distributed automatically in the checkboxgroup columns.

{
                    xtype:'checkboxgroup',
                    id:'randomId',
                    fieldLabel: 'CheckboxGroupLabel',
                    autoScroll:false,
                    labelSeparator : '',
                    columns: 2,
                    items: [
                      {
                        boxLabel: "CB1", 
                        name: "CB1".toLowerCase(),
                        id:'CheckBoxId1'
                       }
                      .....
                       {
                        boxLabel: "CB9", 
                        name: "CB9".toLowerCase(),
                        id:'CheckBoxId9'
                       }
                     ]
}

Now I need to show checkbox1 to checkbox6 in column 1 of checkboxgroup and from checkbox7 to checkbox9 in column 2 of checkboxgroup.

Is the above case could be possible ? Please help on this if anyone have come across this scenario.