I don't know of a sand sifting species that would survive long term in a 29g. They sift because they are always eating. A sand sifting species that might do well is a court jester goby. They grow to a maximum of 3". And since they are captive bred you may have a better chance of getting it to eat frozen foods. They will also pick at little strips of nori you can attach to some rock on the sand. Live Aquaria sells Biota captive bred Court Jester gobies. Going Captive Bred can relieve your conscience a little if it doesn't last long term. Aquaculture Nursery Farms or Algae Barn sell Tisbe pods and if you haven't done so already I would seed the tank and perhaps add more every few months. You can also pick up this Brine Shrimp hatchery which is the best design I've seen yet. Feeding live brine will go a long way to the health of your fish and coral. The beauty of this hatchery is it's dirt simple to use. No air bubbler needed and no worry about eggs and shrimp mixed together.
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You could make a little brine shrimp feeder like Paul B uses to get the brine down to the bottom of the tank. I think between all of those techniques that fish could do well long term in your tank.
Of course you could also consider a goby/pistol shrimp combo and the shrimp will keep your sand turned over pretty good. This would eliminate the challenge with sand sifting fish.