Canola, with its tuning plugin for chinook (http://repository.maemo.org/extras/p...tuning-plugin/) took a different approach; they edited uri-defaults.list to run their python program, which gave a list of adding the feed to Canola/the RSS feed reader, instead of the RSS reader when clicking the RSS icon in browser-ui. But it does seem hackish IMO and there should be a better way than that, but I don't know if it exists in all honesty.
But for those podcasts that use those special protocols that you mentioned, this post by conny (albeit being C-oriented) may be of use: http://talk.maemo.org/showpost.php?p=312336&postcount=8