What is the recommended process within FSM to account for and process the ordering of backordered parts from an estimate?

Example case: A field tech generates an estimate for a customer on-site that requires parts that are not on-hand and the customer accepts the estimate on the spot. The appointment must be rescheduled for a later date, but how can this be coordinated to a backorder PO? The accounting process really breaks down for me here in FSM... Also, with status bar variable not able to be edited, I can't create a "waiting on parts" hold for a work order appointment.