Ive been researching everything for the tank and the Betta, and found on some site a clear shrimp tunnel. The tunnel allows the shrimp to feel as if they are hidden/safe (radar tells them this), yet are still in view. I dont know the size of the tunnels, nor the shrimp size, but perhaps this would work for a while.
Poor shrimp, lol. What a shock to get sharked by your tank mate!
Oh, perhaps having a school would help. Some people do report it works out, but i think you would need a bigger tank.