Maybe try a trap of some sort. Works for fish, I think it would work for shrimp.
My method is just a large glass jar or beer glass with a plastic ziplock back over the opening. cut the corner off the bag and have the cut corner protrude into the glass, just slightly big enough for the shrimp or fish to enter (like a clear funnel). Stuff it with mysis or something they can't resist and wait. Easy to go in, but getting out is tough because the usually go up or down, which would get them caught by the bag. It works for fish, so I would imagine you might be able to get your shrimp in there too.
EDIT: i have also taken a water bottle and cut the top funnel off, and then inverted the top into the rest of the bottle... same principal.