Just add a sewing needle or 3D print a long thin cylinder.
This is great for spools with small hubs. If your spools have large hubs you may need to print the spacer included, depending on your spools, you may need to adjust the spacer. Keep the center the same size and scale the outer rim as needed for best results.
This is for the 1kg or less spools. It may support more, but use at your own risk! :P