Some bristleworms are also good at sand sifting (though most hide away in rockwork). If you have none in your tank, you could buy some on eBay, but I have always had them hitchhike on live rock.
Sand dollars are technically an option, but they deplete sandbed biodiversity and subsequently starve, like Horseshoe crabs and Sand-sifting starfish. You could try feeding them sinking pellets, but I would just avoid these three sand-sifters in most cases.
Finally, Cleaner clams require frequent phytoplankton dosage, so they would also not be ideal.