1. Possess an item in your inventory that is not persistent (that is, will be picked up by the server after some time)
2. After a few days, or however long it takes for the server to start cleaning up old items, place the item on the ground temporarily.
3. Eat something. This is just what I'm typically doing when I place an item on the ground temporarily.
4. Return the item that was placed on the ground in step 2 back to your inventory.
5. In around 10min. (maybe less) the item will be removed from your inventory.