Creating a Dictionary plugin that fetches data from a server

I want to write a plugin for the Dictionary application like the Wikipedia plugin—one that fetches data for an entry from a server and transforms it. Unfortunately, the Dictionary Services Programming Guide from Apple only talks about static dictionaries, and I can't find any documentation on the entire Internet that talks about this either. There's not even a Wikipedia.dictionary folder in my /Library/Dictionaries folder.

Is this a strictly custom built-in feature of Dictionary.app, or is it possible to create my own dynamic dictionary?