If that's what he wants then he should put it in the licence.
But then the problem would be that it probably could not be on PyPI, since by putting it to there you grant users the right to do stuff with source, including distribution.
"If I upload Content other than under an Included License, then I grant the PSF and all other users of the web site an irrevocable, worldwide, royalty-free, nonexclusive license to reproduce, distribute, transmit, display, perform, and publish the Content, including in digital form."
https://pypi.org/policy/terms-of-use/
(first pointed out here: https://news.ycombinator.com/item?id=27507770)