Change Customer File Maintenance to provide fields on the "Miscellaneous 2" tab that will allow the "Sales" and "Cost of Sales" GL accounts to be specified.
In Create Invoice the handling of System Option #27 - "Break GL postings by invoice" has been changed so that, if the customer has been configured to carry one or both account assignments, then those values will automatically be assigned to the Invoice.
These features will only be available when System Option #27 is enabled.