What they could do is that the live Saturday show could be extended to an hour.
The first half hour, would be a live task, given someone immunity from nomination that week, and guarenteeing someones place on nominations.
Straight after that in the second half hour of the show, could be live nominations, with just one vote per person (In the event of a tie person with immunity would have casting vote). This would ass more tension to the show making the tasks important, and still leave in nominations and the public vote. By also having people up for the chop, by means of the tasks, the 'boring' people, who no one nominates would be up more often and could be evicted eairier on in the series.
Stright after the show the lines could open, maximising phone profits for Channel 4.