Direct Tax deductible items and automatic posting on extended ledger

[Tony8]

Dear All, 

I have a question about direct taxes configuration and automatic posting using parallel ledgers, suppose I have a commercial ledger 0C and a standard Tax Ledger 2L, in addition consider that I have an extension ledger TA on the top of the 2L. Let's start with this simple scenario: 

1) I have telephone expenses that are 80% tax deductible, it means that on the tax P&L I should have a cost on teelphone expenses of 20% less, i.e. 1000€ on OC it would mean that I have obtain with an automatic posting an adjustment on the 2L or TA of 200-. How can i perform this steps in a structured and automatic way whitout using the SAP Profitability and Perfomance Management tool? I hope the question was quite clear. 

Thank you

Kind regards

AG