Workflow to set costing method to specific for serialized items

With 2014.2 Netsuite now allows serialized items to have average cost.  Nice, but there can be only one default costing method for items and we want serialized items to continue to have specific cost but create far more non-serialized items than serialized ones, and we create something like a dozen items a day.  (Yes I have filed a case/enhancement request about this).  In the meantime some % of the time our people don't change the costing method and create an item incorrectly - *and it cannot be corrected by edit*.

I created a workflow to catch this issue. At present time the only action it can perform is to return a user error, not allowing the item to be saved.  I would like to have the workflow set the field value for the Costingmethod to be Specific.