Embed Existing Face Recognition Tags in Picasa Mac OS X

Picasa 3.9.x allows us to embed the face recognition data into an XMP tag on our photos. At long last. However, Google in their wisdom decided to not make this retroactive. Meaning all your existing photos will NOT have the face data embeded even when this feature is activated. Only new photos will get the desired embedding. What follows is detailed instructions on how I (and many other people) have embedded the face recognition tags into existing photos.