Anyway to have Group By and Total in PDF SUBSELECT

I have an invoice-like PDF Report (1 Master Record - Customer AND Subselect records - invoice details)

Is it possible to have “Group By” (I want to “Group By” months) and “Total” (obviously, total for all in voices in each month) in Subselect. This would be similar to Grid with group by and total.

Any help would be much appreciated.

Capecode