Running Yarn offline

I have a production server Running Rails 6 (latest version) that is extremely locked down. I don't manage the infrastructure surrounding (firewalls, IPs, etc...) the server. Only a few things are allowed to connect and pass through. One of the challenges I'm facing is Yarn. Yarn seems to be tightly integrated into Rails 6, this is fine if the server can connect to the Yarn package repo but becomes a problem/nuisance when it can't. I've tried following this from Yarn without any success.
https://classic.yarnpkg.com/blog/2016/11/24/offline-mirror/

Whenever I run Yarn install --check-files, it returns 'can't connect ... ' or something like it, which is expected. If you need to precompile assets, open the console (rails c), and so on Yarn wants to run.

Any thoughts/guidance anyone can provide in managing Yarn on this machine would welcome.