I have not personally tried this, but I have read where others have had success with the following....
Put a small amount of food into a piece of panty hose, tie it off in a knot, and put in near where you are seeing the bristle worms. Check it late at night. Snails, crabs, etc. will be all over it, but bristle worms tend to get their "bristles" snagged up in the tiny mesh netting of the hose. This will give you time to scoop them out of there before they can figure out how to untangle themselves.