Aside from Balance Forward Billing which doesn't support customizations how could we consolidate/cus

We have a type of customer that has 10 or so locations.  The 'contract' is to bill 1 time a month with terms of net 15 (usually for all activity for a  calendar month) .  

We ship product, from a proprietary softwared, sometimes several times a week to one or more of the locations resulting in charges for qty * product price.   

At time of billing additional  summary items are billed for each location consisting of a one time monthly fee plus a 'handling' type charge for sum of all qty shipped time a dollar amount (say 2.00) 

The A/R folks are manually creating 1 invoice with 3 lines for each location grouped together.