Technically, no - at least not with the rules the way they are supposed to be as of June 1, 2009. If you are going to PACS with anyone in France, both partners are supposed to be in France legally on some level of carte de séjour that allows them to be resident in the country.
You may want to check with the Tribunal de Grand Instance in the departement where your PACS partner-to-be is living. They may have more information about what residence documents they expect when concluding a PACS.
Cheers,
Bev