I've been using the Stop Aiptasia syringe applicator. It's the perfect size. The opening on my turkey baster is way too big and can't hold anything in.
But don't listen to me. My mandarin hasn't eaten yet. I've even shot a syringe full of tiger pods his way. What typically happens is I shoot Ova, chopped Hikari bloodworms or Cyclop-eeze in front of him. He ignores it. Then my blood shrimp, hermit crabs, and snails come over and he'll swim a few inches away to avoid being stepped on and crunched.
Have you tried setting up a "mandarin diner" with a glass jar? Place the food in the jar. It is suppose to let the mandarin eat at its own pace.