How about a section on suggesting tasks for the housemates? Say, once a week people provide just one idea, the 'list' is open for a couple of days (?) and then we can all vote on which one we think is the best. Whichever one wins we can e-mail to Ch4 and see if our idea gets chosen.
I seem to remember that in the previous series they were asking for viewer participation and ideas - certainly for tasks. Any good?