Basically just an idea I got from people talking about training their axies etc, and feeding them in certain places.
For the food - some of it WILL float out of the bowl or miss the bowl, but be in the general area of the bowl. This is actually good to begin with because in a kinda hansel and gretal way, they follow the trail tofind where the bulk of the food is (bowl) by picking up the stuff that came loose.
For what I'd suggest using - pretty much any of the stuff you normally feed your axie, except floating foods.
So - pellets can be dropped into the bowl, As can earthworms and liver/heart (if you use it, mine is a rarity) For black worms I use the pisces packets, so you can put the nozzle right in the bowl and squeeze gently (I usually use half a packet of that and some other foods) so they squirt into the bowl. Frozen blackworms are the hardest, but I put a cube into a shotglass, about 1/3 full with tankwater. Wait for them to defrost completely, then cover it with my fingers, let it slowly fill up on the surface, then (while still covered) put it right over the bowl, letting them float down out of the shotglass, into the food bowl.
Because of the location of the bowl (see my other thread with full tank pics) it means that anything that gets away/floats away doesn't go too far, and doesn't get caught in hard-to-syphon-out places.
You'll get a little sand in the bowl from time to time, but you just syphon it out as well.
Hope that helps