I use a glazed ceramic bowl. They usually come in sets of three, for mixing cookie dough or other baking stuff. I use the smallest one of the three, and you can get em cheap at dollar stores.
This way, it's heavy enough so that if they miss, their tongue doesn't move or shake it like a deli-cup and spill all the feeders which defeats the purpose lol.
Also, being ceramic, I don't have to worry about them trying to catch bugs through the clear sides of a deli-cup, which can cause injury to the tongue if they do it too much.