If the material valuation classes cannot derive the GL account then you need to change the account modifier of the movement type.
the standard account modifier for goods issuing a sales order is VAX (GBB).
Create a new movement type (copy 601) and change the account modifier for GBB to be ZZZ.
From the SD side of things you will need to derive this different movement type.
The standard movement type 601 for goods issue is assigned in transaction VOV6 against the schedule line category CP.
The CP schedule line category is derived in the sales order from the config settings within table V_TVEPZ. This gets mainly derived from the item category used in the sales order...so one way to do this would be to
create a new sales order type
which will then derive the correct sales order item category
which will then derive the correct sales order item schedule line category
which will then derive your new movement type (which contains the new account modifier - which has been assigned to the different COGS account in table T030 under GBB ZZZ).