There are hints in the BUILD dictionary, see python_requirement and python_requirements: https://www.pantsbuild.org/build_dictionary.html, but to add the wheel directory - assuming its within the repo or at a known fixed path across repo cloners, in pants.ini:

[python-repos]
repos: ['%(buildroot)s/wheel/dir/inside/repo', '/wheel/dir/path/guaranteed/on/any/clones/machine']