Dynamics AX: How can corrected tax be coded in the Invoicing Input / Update of Purchase Orders - Posting Function?

Question

Corrected Tax has coding support in the LedgerJournalEngine but this functionality is not available for invoicing update via the Purchase Order Screens.

The scenario is as follows:

On the invoicing screen of the Purchase Orders I want to add a field for corrected tax per invoice line. Corrected Tax must override the default tax calculations only when corrected tax has been entered. The calculation should be as follows:

(Price * Qty) + corrected tax = total line value.

What is the easiest way to accomplish this and the results must carry through to the General Ledger?

Many Thanks for your help.