@elberet, I would see this working as a user tweeting to an account that’s associated to the forum with the hastag being the topic ID.
So, for example, an RSS Feed can pull new topics and distributed it as a tweet to all followers with the topic ID as a hashtag.
For this topic it would be something like this:
@forumtweeteraccount #20332 The remaining number of chars of text would be tweeted plus a http://shortened_link_to_the_post