Endive wont work than, you can only keep this up till 2-3 days...
What about chicory? Here is a duck snack list. Maybe you'll find something suitable ☺️
Hi Quasi, welcome to BYC!
My ducks love to stick their bills in a head of endive... you could hide some mealworms in there so they have a reward in a reward.. a granola bar for ducks, I don't know...