I feed mine a variety, but he really swims for live river shrimp. The smaller ones he has difficulty catching so, if possible it might be an idea to try dropping a few of those together with some larger ones on the other side of the tank (the side he doesn't like swimming in) see if it'll entice him over there.
River shrimp dont last particuarly long if you dont have a spare tank as they are high ammonia producers, but if you are able to get 10 or so from your LFS, it might be worth a try.
Best of luck.