What is currently the recommended way to mirror a Private Docker Registry?

Mirroring functionality is provided by official docker-registry image but only for the Public Registry.
See [documentation](https://github.com/docker/docker-registry#mirroring-options):
"Beware that mirroring only works for the public registry. You can not create a mirror for a private registry."

My use-case:
A bigger development team that is working in an office with a limited network. They only pull docker images from registries. Pushing is occasional and handled by Jenkins box hosted in AWS. Most of the images they use resides in our password protected Private Registry (served over https). So it's only natural to mirror/cache the Registry on a machine in a local network. If not for https I would just go for HTTP\_PROXY and local squid install.

I'm sure I'm not the only one solving docker dev bandwidth problem. What do you do?