sale line provided by 2 storage locations

Hi Gurus, I need your help on the following point:

I have 2 storage locations, each one with a different shipping point. The same material can be storaged on both st locations at the same time (partial quantity in each st).

Then, when I make a sale, SAP has to take the desicion and take stock from the st location that has the material. If it is partial quantity, then I need that sap creats automatically 2 outbound delliveris, one of each st location.

But, according with I saw .. SAP needs to determine this on the sales order .. I need to enter the shipping point on sales order, and make the dellivery from this shipping point only (wich is, one storage location).

As the shipping point is at dellivery item, I can´t make more than 1 schedulle lines with different storages eigther ....

I tried making a Z program on the copy control rutine but I found that I can´t see the available stock in each storage location, so, can´t determine where is my stock .. I have MRP at plant level...

Can you help me on this? thanks in advance!