Deferred Billing

Is anyone out there doing Deferred Billing where a Sales Order line is shipped full qty but you are only invoicing the Customer for a portion of price at shipment.

We currently do this by doing a Customer Shipment for a partial (fractional) qty (e.g. SO line qty = 1 but we ship a qty of .33) this then generates the Invoice for .33% of the Sales Order Line price. At a later time we then create another Customer Shipment for the remainder or another .33 qty until we eventually Invoice the customer for the full qty/amount.

Our EA UOM currently allows decimals to allow for fractional quantities. We are now looking at the Epicor Serial Number Tracking and need our EA uom to be whole numbers. We are looking at other ways to handle Deferred Billing and wondering how others are doing this?