1. Choose the item that you would like to store.

2. Choose to sell it on market for an unreasonably high price unlikely to be bought (which is also a reason why you should better store items with low market value, so you don't spend too much gold on commissions).

3. Put it to sale on market for the shortest amount of time.

4. Nobody will likely buy it, after sales time expires the item goes to... your market storage. It has no apparent limits.