I have the same problem with shrimp stealing from my anemones (I can see a definite benefit to anemones having clownfish to protect them from raiders). I usually have a "stick" (piece of rigid air hose) that I use to discourage the shrimp until the anemones can get the food to their mouths.
It's better when I feed the shrimp in a far corner then feed the anemones a little extra. They get most of it themselves. But that means keeping my skimmer and GFO reactor running full speed.