You can't. If you buy an open warehouse, the exchange will give you a warehouse receipt on the delivery date, and you can take it to the designated warehouse to pick up the goods. If you sell the open position, you need to give the exchange warehouse receipt before the delivery date. The way to get warehouse receipts is to buy them in the market. This is usually done by futures companies. If you provide the goods yourself, you need to go to the warehouse for acceptance.