No, there is no direct way of scraping PDC's.
If you are wanting to salvage some of the materials in the PDC you will need to abandon/self destruct the PDC and use a salvage ship to salvage from the resulting wreck.
Also note that(unless it has been fixed in a recent version) the refit PDC order doesn't actually refit the pdc when it is completed, instead leaving it with the old design. This can be worked around by altering the old design to match the new one, then viewing each pdc via the ship details screen will update them to the changed design.