Clearing of invoice (incoming payment) based on due date in installment payment terms

Hi

In my current client I am using instalment payment term in Sales invoice. During billing, the customer line item gets divided into different lines with different due date. This invoice will be cleared manually through F-28 over the period of time.

The issue is that the client wants to clear these line items AS PER THE DUE DATE. He wants us to ensure that the invoice line item which becomes due first should be cleared first. The system shall not allow the user to clear the invoice line item which is due later before clearing a line item with prior due date.

For ex, if instalment of an invoice is due on 21.05.2012 and 21.06.2012, user should not be able to clear payment for 21/6 before clearing inst of 21/5.

I am not very sure of how it can be done through standard system. Please help

Thanks

Sourabh