Offline build for NixOS

I am currently trying to create a native vimPlugin implementation for NixOS for vscode-js-debug. Now there are some specifics which make building node related packages pretty hard on NixOS. one is the nature the package.json being non deterministic which goes against the basic principle of the way NixOS operates. Also a package-lock does not guarantee the packages have not been altered (version deleted and republished).
Adding to this principle. NixOS does not allow network access during the build process. This is the tricky part for this one as npx gulp vsDebugServer does rely on internet access.

I am more than happy to provide a PR addressing the issue. However I do lack experience with gulp. So it would help to get some assistance here. I also saw that there is a task called dapDebugServer and was wondering if that would already do the job as it does not seem to include the i10n download nor compile:dynamic which also causes some trouble due tue dynamic linking.

I did find that in the gulpfile.js the l10n bundle download is an example that relies on downloading the zip from a github repo. My suggestion would be that you could set env vars during the build process that specify the location of such files. Would this be a viable option or are there any roadblocks I did not think of that would make an offline build impossible?