By an equivalent option in setup() of course. I'm not against the
*functionality* of MANIFEST.in but on that (a) it's a second file you
have to remember to write and maintain in addition to setup.py (b) has
its own ad-hoc syntax instead of python and (c) overlaps in scope with
the package_data and data_files of setup.py.

FWIW I wrote a module that overrides the default build_py and sdist
commands with versions that allow specifying package_data recursively
(while preserving file permissions, unlike the - buggy IMO - behavior of
distutils) so that I can get rid of the MANIFEST.in.