Nigel did not really have much to add. He guessed you could try a permanent stick on the Chort's legs if you were fast enough. But you would need to be really really lucky. Though to be fair you would be lucky if any spell would hit Chort.

You could just aim the freezing charm at the legs also. Maybe Nigel was taking to too literally and it was just the leg locker curse or Jelly-Legs Curse. But those seemed too easy an answer.