[steveklabnik]

  > Sorry for pestering again

No worries! This thread is a bit old but I'll try to pay attention to it.

  > From what I see in the cargo source the crates.io URL is hard coded.

It's not: http://doc.crates.io/config.html#configuration-keys

TL;DR:

  [registry]
  index = "URL_GOES_HERE"

and you're good.

  > It's not about that either because the commercial repos contain very
  > much the same OSS packages as the standard repo but don't present all 
  > of them to everyone all the time.

Ahh yeah. What I mean is, you'd have to set up the packages in that registry yourself. Which sounds like what they'd want to do, so seems fine.