This report would be easily handled using Sage MAS Intelligence and the Customer Sales report that ships out of the box.
All you would need to do is run the report for the chosen date range, modify the pivot by dragging the sales rep into the column area and remove non-required data elements such as qty, costs etc. leaving just the total invoiced amount, and then this layout could be stored permanently as a template using the Sage MAS Intelligence create and link template function.
Not sure if I am missing something, but this would be very simple to accomplish using SMI.
