for fanpages/businesspages:i know i can prevent users from posting new posts - but how can i prevent them from commenting existing posts ?

i create a fan-pages of a sportsclub. the page only has a wall - where all posts come via RSS Grafitti from a RSS feed. it's just a way of spreading news - the sports club does not want any comments - since there's nobody who has the time to moderate this posts.

any idea how to do this ?