Adding CC and IPTC-Extended XMP fields to Lightroom Metadata

Seeing how as Adobe is the original author of the XMP standard, I'm hoping that Lightroom allows one to take full advantage of the extensibility of the its metadata framework - allowing one to annotate photos using, for instance, the Creative Commons licensing fields defined here: http://wiki.creativecommons.org/XMP and the IPTC-extended fields http://iptc.cms.apa.at/cms/site/index... like PersonInImage, which are already understood by Phil Harvey's free Exiftool. I've so far been unable to figure out how one would tell Lightroom to use these metadata. Am I missing something?

If not, for the moment, I'll be sticking with the (much cheaper!) combo of Apple's iPhoto and Holocore's PictureSync.