Advance Billing with Advanced Fulfillment

We are an IT service reseller and we use billing schedules for all our sales orders. Whilst customers often place orders for multiple services on a single sales order, items are fulfilled at different times (often over a number of months as services from our suppliers come online). Netsuite is limited in that once you fulfill one line item with a billing schedule, Netsuite fulfills all other lines with a Billing Schedule which is a problem if only one item on the sales order is ready for billing. We can't sit and wait for all lines to be fulfiled as