IMO apply a posting system to Might. You start losing might if you don't post enough (Say, one post a week or every 2 weeks), and you get bonus might if you post plenty. (And not filler, GM discretion if it advances the story and gives you might)

EDIT: And to prevent someone from posting once with no real detail and just filler, and then vanishing again until the time limit, they have to advance the story with the post.