I know of no way to dupe weapons, however the Blade of Winterhold needs no Duplication as it's yours.
You can still duplicate apparel in 1.9. The Method:
Place armor on mannequin. Exit the house. Returning, and removing the desired armor, and exiting the house again. Upon returning the original set of armor will still be in the mannequin's inventory.
I do not believe it works with a quest item such as the Helm of Winterhold, also duplicates of self enchanted armor will lose the enchantment.