Personally, the way I would handle this would be to build a cursor of all the invoice totals you need BEFORE you run the report.

So...

SELECT invoice,SUM(dollars) AS invdlrs,CNT(*) AS numlines ;
FROM invoices ;
GROUP BY 1 ;
INTO CURSOR invtots

INDEX ON invoice TAG invoice

SELECT invoices
SET RELATION TO invoice INTO invtots

Now in the report, you can just reference invtots.invdlrs for the total dollars in the invoice at any time you're processing that invoice.

--Brad