Invoice Line Number = Sales Order Line Number

I need to have invoice line numbers match sales order line numbers even when the sales order lines are not shipped at the same time or on the same day.  It seems if all items are shipped at the same time, this can be accomplished with line ordering rules.  However, this does not seem to work if items are shipped on different days.

For example, suppose I have a sales oder with 3 line....Line 1, Line 2, and Line 3.  Now lets say that Line 3 ships today and nothing else ships.  When I run Autoinvoice, I need the invoice to show Line 3 so that it matches the sales order line.  This is key as I have customers trying to match invoice line numbers with sales order line number and they are not paying because the line numbers do not match.  HELP!