Lowering the gain / volume of ALL the esses by hand is very time consuming but IMHO gives the best result with no side effects ( i.e. a de-esser can make someone sound like they have a lisp )
An easier way might be to use the split tool to separate them all then drag them to an adjacent track that is set lower in volume, this can be a lot quicker than using automation or clip gain to make individual edits.
In Cakewalk you can ensure the clips don't accidently slide to a different time by holding down the shift key as you move them, so they will stay locked in position.