Offline SW update - Azure Sphere

We are using Azure Sphere devices in different conditions. Most of the devices are constantly on a network which provides internet. However we have a significant number of devices on On-Premis setup, which does not provide internet access. These places are generally underground, or on places where providing a network (with internet) with sufficient throughput is problematic.

We are looking for a solution to overcome this obstacle - we would like to update the image packs of the Azure Sphere devices OFFLINE.

Is there any solution for easily update the firmware offline? For example, download the image packs and then create a virtual-local IoTHub instance, that could help to deploy the new image packages.

Current solutions, which are far from optimal:

• update with azsphere cli commands - very bothersome, and hard to do as we are deploying - updating multiple devices at once (number can reach 100 easily)
• use multiple repeaters or very long Ethernet cables - again, its working, but sometimes a reception is still bad, and software update take hours