Silly question (substrate)

I was so busy trying to put all the plants in water with lights pointed at them that I totally forgot that the tank I put my new shrimp in is bare bottom. Now, the glass does let me see nice mirror images of shrimp hiding under stuff, but the shrimp seem kind of skittish. I assume that putting something on the bottom would make them feel more comfortable, but - how the heck do I get it in there without crushing the poor shrimp? I'm not used to delicate critters!

The shrimp are Neocaridina heteropoda in a 20 long, half full of water with floating plants and some moss. They have an assortment of ghetto hiding caves and a sponge filter. I wasn't planning on planting the tank, just adding some inert black sand (or I was thinking about using oyster grit for small birds - they could use the calcium carbonate and the look is interesting to me)- but I totally blanked until after the shrimp were in the tank.