I've never had much luck with forceps feeding with blackworms; they are too small and wiggly.
Unfortunately, most feeding dishes do not hold them in, so they all crawl out. Worse yet, blackworms + soil = major foulness, which has been known to poison the sals.
I have 2 solutions to this problem. First, I put the dish of worms on a bare area of the tub, so that the escaped blackworms crawl under the dish and are easy to wipe up off the plastic. If I'm using a paper-towel setup, I clean the towels frequently. Second, I have devised some DEEP feeding dishes that the blackworms do not normally escape from. If I get time, I'll try to take a photo and post it.