Could make the mannequin composed of several different pieces that can be glamoured, so the actual item stays in the armoury chest/retainer while still visible. Or could make an inventory for this kind of things, accessible from a special chest... Or as Blindheart said, make us trade the pieces or craft the mannequins using the gear as mats... there's plenty of choices, I just would like to be able to display all the wonderful gear that is in game.
With tha armour log confirmed though, I'm afraid it will be a long time before we can see something like this... But I'll be happy with the log too, especially if they do add some lore to each piece!