Availability check

We have following scenario.

There are certain products which are made to order (production is made only against order and stock is account assigned).

Sometimes there is a surplus production against some of these sale orders (expected rejection not taking place). This stock is then removed from sale order stock (account assignment is removed) and put into unrestricted stock.

We want to check this surplus stock against new incoming sale orders (during creation or otherwise) and if available, assign it to the sale order.

How can we configure this?

The requirement type in the sale order is VEKS.

Regards,

Nitin Thatte