You just have to click an item, so that it will get "glued" to your cursor. Then I hit ESC and restore a saved game. The saved game loads and a window appears saying that if I drop the item, it will be lost. I select no, and place it in my inventory (or quick slots). There it is: duplicated item.
The best part is that it doubles stacked items, so if I were holding 8 potions, I'll end up with 16 potions!!!
