I had a similar issue, i used nets and pipe/tube cleaners to coax him into a corner of my tank and then netted him. The pipe/tube cleaners are useful as you can bend them in and around the rock work. Just use them to poke at the shrimp, the shrimp will get scared and swim away. Just keep moving the pipe/tube cleaners closer and closer forcing him into a corner and then net him. If you find places where the shrimp keeps returning to hide, put a few pipe cleaners directly in the area and the shrimp will avoid going there. It takes some time and practice, took me about an hour. As long as you don't have any hidden spaces where he can avoid the pipe/tube cleaners, it will work. It might stress the shrimp, in which it'll pop off its big front arms, but they grow back.
