"Shadowing" upstream repositories

Hi there, We're using devpi in production and we have some internal libraries that we don't really plan on releasing to the public. Some of them are named in a way that clashes with pypi's upstream packages (though they are in no way shape or form related). How can I achieve this with devpi? I wasn't able to really get a clear answer and the documentation on "shadowing" -- which is presumably what this feature that I'm inquiring about -- says "TODO." :) Any tips would be appreciated on how to workaround this issue! Cheers & thanks for devpi! Mahmoud