How to add private PyPI dependencies to a pixi project?

[Yura52]

In some projects, there is a public part for general audience and a private part needed for development of the project. In my case, this private part involves proprietary PyPI dependencies that I cannot share publicly. Roughly speaking, in my manifest file, I have something like this:

[feature.private]
pypi-options = { extra-index-urls = ["<private URL>"] }
pypi-dependencies = { <private packages> }

[environments]
private = ["private"]

Is there any way to maintain this private environment without explicitly listing its details in the manifest file? In particular, I may be ready to consider solutions that will go slightly beyond the "official" environment model of Pixi. For example:

[feature.private.activation]
scripts = ["install_private_pypi_dependencies.sh"]

Are there any better workarounds?