I thought this was interesting:
https://www.ebay.com/itm/Rb67-Mediu...096439?hash=item2ae75a8837:g:a~kAAOSw~rxepxJQ
Pictured:
The Description reads:
Rb67 Medium Format Instax Mini Film Backs. Condition is Used. Shipped with USPS Priority Mail. Each holder will accept 2 sheets of Instax mini film which you unload from the Instax packs in the dark and load into the film holder. Film holder locks to the rotating back just like the standards film holder does. Cock shutter, remove dark slide, expose, replace dark slide, remove Instax sheets in the dark, reload into the factory Instax pack, and develop in your Instax mini camera in the dark with the flash and lens covered.
I have no connection with the product or the seller, but thought that it might make good use of all those 220 backs out there.
https://www.ebay.com/itm/Rb67-Mediu...096439?hash=item2ae75a8837:g:a~kAAOSw~rxepxJQ
Pictured:

The Description reads:
Rb67 Medium Format Instax Mini Film Backs. Condition is Used. Shipped with USPS Priority Mail. Each holder will accept 2 sheets of Instax mini film which you unload from the Instax packs in the dark and load into the film holder. Film holder locks to the rotating back just like the standards film holder does. Cock shutter, remove dark slide, expose, replace dark slide, remove Instax sheets in the dark, reload into the factory Instax pack, and develop in your Instax mini camera in the dark with the flash and lens covered.
I have no connection with the product or the seller, but thought that it might make good use of all those 220 backs out there.