Permanently dupe one item.
A mannequin can duplicate any one piece of visible apparel (armor, clothes, rings, etc) indefinitely. To do this, go to the mannequin, store the visible armor, and exit out the menu. The mannequin should disappear, pardoning the hands. Go back into the mannequin, and equip any other piece of equipment that is a different type than the one you want to dupe. (if you want to dupe a chest piece, do no put another chest piece on it). Then exit out of the menu. The mannequin should still be invisible. Go back into the menu, and take back the piece you want to dupe. The mannequin should become visible with the second piece of armor on it. Leave the area, and re-enter. Your mannequin should be invisible again. When you check it again, it will still have a copy of the armor that you took off of it. Exit and re-enter whenever you want another copy. One thing to note, is that the mannequin will now always have that one thing on them, and I have yet to find a way to change what it dupes. So basically your one item will be "Imprinted" onto the mannequin permanently. Voila!