For transmogrification we need an Item model journal which behaves precisely like the Mount and Pet journals.
Right-click and 'Add to Item Journal' teaches you the model. You can then vendor the item and retain knowledge of its model.
"You already have knowledge of this item's appearance." if you have it already - especially useful for items that share models.
Transmogrification now draws from the Journal instead of your bank, bags & void storage.
Done. Ship it.