get a long skewer and stab on a frozen silverside... then shake it around to make it look like it's swimming, that will usually get them. If that works, you can eventually get him trained enough to understand that when you come around, he gets food. Also, make sure you aren't feeding too often, because these predators don't typically eat more than a couple times a week, but it's a lot at once. If you don't have any luck at all, maybe think about getting around 30 ghost shrimp at a time and setting up a bucket with a sponge filter or airstone in it. Feed the ghost shrimp a marine pellet food, and when they're gut packed, feed them to the lion. That should be the most nutritious live food you could give him.