Prorate MO Variances

When you close a manufacturing order (MO) any values remaining in the WIP accounts are moved to their associated variance accounts.  Standard cost accounting says the most accurate way to dispose of those variances is to prorate, ie redistribute, the amount according to the percent of quantity in inventory and to COGS for what’s been sold.  Is there an easy way to do this in GP?  How is most companies handling these variance accounts on the financials?

Thanks!