Serial Track Parts-on-the-Fly

Has anyone ever tried to serial track a part-on-the-fly order/po line
I'm guessing it is impossible.
In case you are wondering why we are wondering: We've discovered that
Average costing does not behave how we thought it would. If we have a
generic part number (e.g. WI-REFRIG) that could be any number of
different pieces of refrigeration, the actual cost from the PO does not
come through to the invoice / sales gross margin report... instead the
average cost does - go figure. But if it is a part on the fly that is
on the order line (and thus the PO line) for this buy-to-order part,
then the actual cost (from the PO) flows through fine. But we seem to
need to use a real part-numbered part, since we must serial track our
Maybe there is some other costing method other than STD or AVG that we
should be looking at? Something like a "Buy-to-order Actual Cost"
costing method.

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