When you add the new event, specify one date for beginning date, leave
the time set to 12AM, and specify the end date as the day after, leaving
the time set to 12AM. On the daily view the event will appear at the
top of the list under "All Day". I think that is as close as you can
get.
Example:
Begin: 1/4/2006 12:00 AM
End: 1/5/2006 12:00 AM