Acquire packages from the local file system, instead of a remote http server?

How difficult would it be to add a feature for stack to be able to install packages from a local mirror or a subset of an LTS, without using an http server, but directly getting the resources from the local file system.

The use case is thus:
In my company, the modus operandi is that we have a prerequisites installation, that sets up a workstation with an appropriate environment with everything a developer needs to get working.
We would like to use stack, but we prefer to avoid the added complexity of either running another http server in our network to serve the haskell packages behind the firewall, ala: #2567, as well as avoid the need to use an http server locally on the workstation just to serve files that reside locally anyway.

This could be somewhat similar to #359, only that the cached downloads will be prepared on a different machine than the one that will use them.

I'm currently looking at the source code but it is difficult to get a ballpark estimate in a short amount of time for me, as I don't have prior experience with the codebase.

If it so happens that it isn't a big modification, me or someone else in my company will be more than happy to implement it and submit a PR.