Relieving parts inventory for service work

We're a sales & service company using Sage100.  On the service side, we're currently either buying inventory parts and charging them out immediately to the service department  (this makes for cost in the current month and revenue in a subsequent month), or when doing a repair, we're creating a sales order and listing the inventory parts, thereby relieving inventory when invoiced (this causing a lot of administrative time, plus instead of an invoice showing a single "parts and labor" line item, each individual part is a line item, plus a labor line item).

Question:  Is there a way to invoice a single line item and still be able to relieve inventory of multiple items?  I know that one way would be to create a bill of materials, but that's not realistic when practically no two repairs are alike and therefore you'd be creating thousands of BOM's.

Any ideas or suggestions would be greatly appreciated.

Thanks,

Trudy