I had a guide for doing this, they were plugging an ethernet cable into an ethernet-to-usb adapter (apple brand, plugging that into a powered usb hub, uplinking the hub to a thunderbolt-to-usb camera adapter, and plugging that into the iPad.

Apparently it worked for him. I tested it at home and it worked for me too.

I just tried this today because I had 200mb of apps to download into 20 iPads each. (and I have a caching server on the network too) I got a popup telling me this accessory isn't supported. It looks like apple decided to deliberately pull this wonderful "feature"?

My guess is that there is a proprietary device or software for setting up 'fleets' of identical iPads and that is why they closed your door.