This feature is still under development. We don't know how soon it will be available.
Geoff Rasmussen posted his suggestions on converting sources to the Legacy User Group mailing list in June. You can read his post in the archives at http://www.mail-archive.com/legacyusergroup@legacyfamilytree.com/msg26496.html (If the link doesn't work, try this TinyURL http://tinyurl.com/6kc8hb)