Tearing the sides off of Overture carboard spools works pretty well, but there's the problem of the spool spinning while trying to retract when it gets low. This insert solves the problem by sliding in-between the core of the carboard spool and the Bambu two-piece spool.
Tear the side of the spool off that has the notch in it, slide the adapter inside the spool and seat the tab in the notch. Place the shorter Bambu spool half on the top and flip it over. Tear off the other side and align the tab on the spool with notch on the adapter. Takes a little practice, but once it's together the cardboard core is locked on the Bambu spool.