When you buy them they should come with a mix of maize flour and saw dust over them , the basemix may just clump together once wet from the sweat produced.Once they start to sweat its a thankless task trying to stop it unless you can cool them down , spliting them into smaller containers and placing the conatiners in bowls of water can help , a metal container works best which is why the old timers preferred the old metal bait tins.
You could take some plain crumb ground bait so that if they do turn you can crush some of the casters and add them to the groundbait maybe along with some crushed hemp , this will fizz with some casters floating up to different degrees . (worked for the great Ivan Marks !)