DEBIT (RTS) Invoice payment terms

we have an issue with RTS invoice created by the system after receipts are returned to supplier.

Let me explain.

we have received some qty and system created an ERS Invoice (say..with due date of 01-Dec-2013).  Next day user created a return for same quantity and system created a DEBIT (RTS) Invoice (with due date of 02-Dec-2013).

due to this; ERS Invoice got paid first and DEBIT invoice is pending to offset other invoice payments.  user expects that both invoices paid together with Zero dollar amount.

any option to make RTS invoice payment terms as Immediate instead of considering payment terms from supplier site.  we want Immediate payment terms to be applied only to RTS (DEBIT) invoices.