I'm trying to remember exactly how I did it. I know I used the two boxes so that I had the middle zombie between them vertically on the second from the left column, I just don't remember how I got them there.
I don't see how I can push that one zombie left though. If I do it with a crate, the crate will be trapped. If I do it using water, then the chain won't work
...that still doesn't help. My only option with the crate is pushing them up two, and then it's stuck.
Plus, you said they needed to be in a line. There's no way to get them in a line from what I can see - we still have the problem of pushing one to the left column, which would get the crate stuck.