Hi
How you are reserving the stock at the moment? If this is with availability check then you can go for delivery option. Dont reserve the stock the time of order creation. When you want to reserve the stock against any sale order just create the delivery for that order and don't do the PGI. System will automatically reserve the stock against that delivery in schedule for delivery.
If you want this to be done from availability check then I am afraid it is not possiblt. Because in that check system will reserve the stock against first order.
Check the below link if it is helping for you.
http://scn.sap.com/thread/2068072
Thank$
