Prusament Spool Inside Hub for Refill Spools

Buying refill spools to save plastic, I encountered the problem that the filament is wound to a diameter smaller than the cardboard hub diameter of an empty Prusament spool i intended to use. This seems like a small problem, but I couldn't find any way to enlarge the inner diameter of the wound up filament. 

This hub clamps to the inside of the brim of Prusament spool plates, rather than to the outside like the original cardboard hub. This results in a smaller hub diameter, making the refill filament fit.

I used some poor quality PETG. Infill can be turned off.