Offline build support for packaging

Hi,
I was attempting to package this software for NixOS, and it looks like the cmake makes many network calls during the build, which, for reproducibility, isn’t allowed in NixOS. While it is possible to work around this on the packaging side, any solution would be fragile, so I was wondering if it would be at all possible to restructure the build process so that CMAKE can be run fully offline. I’d be willing to help if needed.