I am not a shrimp expert, but I am pretty sure their primary diet in the wild is lankia and sand sifting star fish. So if you want the A-hole stars to get eaten you probably need to take your other stars out and put them in the sump. Its not from experience I'm just guessing, but I would think even if he didn't fully eat your sand sifter that the shrimp would loose its appetite for the little A-holes and just eat on your sand sifter slowly. Better safe than sorry, you don't want him to eat your sand sifter and then still not eat the ASStrea stars.