Full Offline / closed network capabilities including feed generation

Description of the new feature / enhancement

I have read through various feature requests and documents, but have not yet found a suitable solution.
The problem
We have customers with encapsulated networks, which means data transfer only via secure storage exchange (Mowing Data with Usb thump drives between the networks). We can adapt the manifests so that the data sources are offline, no problem. But we need a feed, and we need to create it within the environment. Directly specifying the manifest for each file, as suggested in microsoft/winget-cli#226, is not an option.
The other previous solution like microsoft/winget-cli#203 microsoft/winget-cli#213 or the article https://github.com/microsoft/winget-cli-restsource is not an option (Due Azure requirements).

Proposed technical implementation details

My wish / proposed solution would be a meta-manifest as a feed in which all manifests can be added. This could then simply be stored on any web server via https and automatically updated with a PowerShell script.

No files, tests, or entry points are named in the issue. Start by reviewing this repository's REST-based package source implementation and the linked prior proposals, then define the offline feed-generation scope and the conditions that would demonstrate a complete solution.