The main point is that you cannot issue from subcontractor stock.
You have to bring it back into normal stock, even it is just for 1 second, and then do the issue from normal stock.
I think your requirement needs an own development, that in sequence does all the various steps (creating sales order, moving subcontract stock to normal stock, creating delivery, posting goods issue, creating bills) by calling BAPIs or call transactions, just so that a user does not have to do all these steps manually, but you wont get around all the needed steps.