Did you ever get a reply to this question
I have this problem, and another. Prior to a customer adding anything to the cart, I want them to select the delivery option they would like; Either Delivery or Pick-UP. This is important because I used two locations (50 miles apart), one for delivery and one for pick-up, and they have different stock. By getting the customer to choose the fulfilment option at the beginning, I can then present the different stock to them.