What about registering the project names on the public PyPI, and not giving the credentials to anyone? This would work well in case you have a definite list of project names. There is also the added benefit of avoiding clashes when two projects of the same name exist on public and private repositories, which might cause issues during dependency resolution.
But I am not sure what is the current etiquette regarding name squatting on PyPI.
It feels like it would be nice if one could reserve a full namespace on PyPI for their own username and/or organization name (for example all sinoroc.* names on PyPI for me, and by convention, I would kind of have loose ownership of the whole sinoroc.* namespace of importable packages). By the way I am not clear if it is something that will be worked on in the “organization account” feature, not clear at all.