Aww, poor baby. I hope it's going to be OK.
Can you post this to the emergency board also. I don't know who's around at this hour to help out. I don't know very much.
I would try to keep it warm, moist and covered and hope it heals on it's own in the incubator. Could it be the area around the "belly button" where the yolk and blood vessels absorb just before hatching? If it is I know I've heard of chicks hatching before that whole process is finished and sometimes they can heal up in 12 hours or so. I don't think there's a whole lot you can do right now accept make sure that no other chicks can get to the injury since they will peck it to pieces.
I'll say a prayer for you and hope someone else has seen something like this before who can help.