How about this:
The group is told by BB to divide in to two groups for a task. One member from each group has to visit the diary room separetly. The first to get to the diary room is unlucky and told that they have to win the task or they are all up for eviction, but they are not allowed to tell the other group members. If they win then all member of the other team are up for eviction.....The task could last a number of days.
This might not work for evictions, but they could do it for a reward thing. Again set over a few days, the winners for that day aare lucky. (rewards and such) Lossing team unlucky(cold showers, not allowed to use pool etc)
Tis only the mad ramblings of an obsessed fan..........