They did give a response in the live letter.

Q18: Do you have plans to implement a feature, such as a book that records items you have obtained once, and you can drop that item but still use it for glamour? With this feature it’ll free up the inventory space.

A18: Yoshida: We have no plans for this. We would increase the inventory space if this was possible.
You're not going to get anything else out of them.