How can I group columns in a grid, while exporting to PDF using AlivePDF in Flex?

Question

I am using AlivePDF for exporting my data in a grid, in Flex. I am also showing the same data on the browser using AdvanceDataGrid, in which grouped columns are also present. I wish to show the same grouped columns in the PDF too. Is there a way to do this?

grid.columns = [{headerText:'Code', dataField:'code', width:22},
                {headerText:'Label',dataField:'label', width:22},
                {headerText:'Last Months',dataField:'lastMnth', width:22},
                {headerText:'Last Quarter',dataField:'lastQtr', width:22},
                {headerText:'Last Year',dataField:'lastFy', width:22}];

In the above code, I want to group the columns lastMnth and lastQtr.