We are using APPS 9.

Our user would like to be able to apply an earned commission on customer A’s account against customer A’s outstanding invoice. 

The invoice amount is $100.00 and we want to apply a commission of $60.00, that is owed to the same customer, resulting in a net payable from the customer of $40.00.  Note that the commission payable has not been vouchered into AP, it is sitting in another balance sheet account, so we cannot use the Netting functionality at this time.  I was hoping to use the Customer Offset process, create a WO code that we could direct to the GL account that contains the commission accrual, but it will not allow me to make a partial write off against the $100 invoice.  I would have to wait for the customer to pay the $40.00 before I could WO of the difference, and the user wants to be able to apply the commission before the customer pays the invoice. Any ideas other than using a manual or instant invoice that would credit the customers account and debit the commissions accrual account?