Add 2 magnets D5x2mm. I use N35 magnets and they seem to be strong enough for a few cables.

Depends on your print setting and precision, but if you print in this orientation, in general the magnets should be friction fit into the holes without problem. If not, add a tiny bit of glue to hold the magnets in.

Can be re-purposed as part of my glasses holder:
[https://www.printables.com/model/1718405-simple-magnetic-glasses-holder-clip-onto-your-shir](https://www.printables.com/model/1718405-simple-magnetic-glasses-holder-clip-onto-your-shir)