Assuming you want Round 5 to include everyone (and not to be snaked), set all of your rounds as prelim/preset. Run the tournament normally. Then, after you enter Round 5 ballots but before you run results, change Round 5's type to Final (do this on the Setup page of each event's schematics). Also be sure that your tiebreaks and sweeps are set on the basis of all rounds.
We run our local IEs the same way, and this appears to work properly for us.