Upgrade Automatically for internal plugins

It seems that for the Upgrade Automatically function to work for plugins they must be “registered” on ww.wp.xz.cn. Specifically, http://api.ww.wp.xz.cn/plugins/update-check/1.0/. Is there spec to this “service” and is there a hook to add a different url? (I.E. We could make a service that matches the “specs” so that we mimic the same functionality)

I will point our that we do not touch core wordpress code. Everything should be done as a plugin, or configuration.

Where I work, we have 4 WordPress sites, across 4 environments, (so technically 8 separate sites) and have a number of our own plugins (custom auth, integration with search engine, stuff that is specific to our environment). As we grow our sites, updating these plugins by hand will become a pain, and it does not seem right to put them on ww.wp.xz.cn when they are specific to our needs. (There could potentially be some IP issues too…)

Thanks for any possible help, but I think I know the answer. (Maybe this is also a feature request in disguise?)