Ability to select multiple clients on invoice/ar reports.

Our firm needs to be able to select multiple clients when creating an invoice report or any other report for that matter. I have Clients with multiple offices, who require separate invoicing terms/addresses.  However, I need to be able to send an inclusive Invoice Report to their General Accounting Office, which includes all of their offices.  The individual offices have to be set up as their own client for more efficient billing purposes, however when I print a report, I want to see all of those clients grouped into 1 total.