Perhaps it could be determined by how long you've been registered on the board then. That might be a more neutral factor than reputation or postcount. Given the board has been open since April 2009, maybe every 2-3 months = 1 bonus point or something.

EDIT: Or maybe bonus points could be determined by things done in the game or something. Like, everyone starts with 10 points, and additional points can be acquired by various achievements or accomplishments completed during the playthrough.