Outside of chopsticks modifications that effectively turns them into a pair of tongs like these, work on their grasp, and make sure their thumb ip is flexed and not hyper extended. That helps a lot.

Oh and encourage them to get thicker chopsticks. I don't know if they use Korean chopsticks (Flat metal sticks) or chinese chopsticks (long with rounded ends) or Japanese chopsticks (short with pointed ends), but I would recommend shorter chopsticks, probably like a Japanese style.