This is something I modeled for a friend of mine in need of a quick adapter which might allow him to use small filament spools inside the AMS.

The holes on the spokes are meant to be used with some sort of retaining method to fix the rotation of the bigger spool to the rotation of the smaller spool, so that when the AMS rewinds the filament on the spool the two spools rotate together. You can use anything you want for this, from a shoelace to a cable tie.

It can accomodate quite small spools, the limit is they must have at least a 40mm center hole.