Importing with RSS importer with custom fields

Hi, I’m in the process of importing the content from my custom database into WordPress. So far this went very well, mostly by using the generic RSS importer.
http://codex.wordpress.org/Importing_from_other_blogging_software#Importing_from_an_RSS_feed

Now I have a category of posts which ideally would use a number of custom fields to display all the content. Has anyone experience with extending the RSS import script to include custom fields?