Uh, interesting method. Violent, but interesting.
how about trying this:
Don't feed your system for a longer period than normal. Then put a piece, single piece, of food where the bristle tends to frequent. Then when he comes to investigate and eat, grab him. Since bristles aren't fast, you can do this. It's worked for me before. But, only because I had the wrong kind of bristle. I like the pink ones. They're good. You may just not be feeding him enough.
Oh yes, and when you do grab him, make sure your hands are protected or use a tool. Hence the name Bristle worm. That and it's bristle like legs.