posting to specific category with flickr

Anyone who is using flickr out there know that you can setup sharing settings so you can post directly from your blog to flickr. But only to the default category, is there a hack that anyone knows about that can change this? This is a very old post about the topic: http://www.benmarsh.co.uk/scripts/flickr-wordpress-category-hack/
but I dont know how to do the xmlrpc.php

Any help is very much appreciated.