DJazz was making something like this with PHP (duh) but a completely client-side program like that requires a ghost player to join. A more sophisticated tool could connect to a special server-side daemon/service that would accept special requests (perhaps on some other port than 10052). This kind of a program could probably be created without having to edit plus, because it would only need to insert commands in the chat. They'd have to go through the plus command filter first, though. Coding such a program without the source code of plus doesn't seem like an unovercomeable challenge to me.