This can be done with any quest that yields an item reward.
Process:
Interact with the target NPC offering the quest reward,
Do not click any buttons in the dialog!
Next step move back from the NPC until the quest dialog is automatically closed.
Repeat the following until you have a good feel of the max distance
you're able to keep the dialog open.
Now this is the tricky part.
You have to click the reward confirmation button JUST before you leave
the interaction distance (see above).
If done correctly you will obtain the quest item and be able to
receive it again by repeating the above steps.
This works because quest completion is broken into 3 parts.
- Item is given to 'Player'
- Quest is removed from 'Player' database
- 'Player' is given gold and XP.