class bdist_egg(_bdist_egg):

    def run(self):
        self.run_command('build_css')
_bdist_egg.run(self)


class build_css(setuptools.Command):
    description = 'build CSS from SCSS'
user_options = []

def initialize_options(self):
    pass

def finalize_options(self):
    pass

def run(self):
    pass


class build(_build):
    sub_commands = _build.sub_commands + [('build_css', None)]
setuptools.setup(cmdclass={'bdist_egg': bdist_egg, 'build': build,
    'build_css': build_css})
Запуск пользовательской сборки setuptools во время установки