Ive done this trick to catch an elusive goby and a snowflake eel, but it takes some time to work. I'm assuming he's still small. If he's a big boy it won't work too well.
Get some PVC pipe atleast a foot long that's only just thick enough for him to enter into.
At each feeding time put the food into the pipe so it's still sticking half way out and let him eat out it, then remove the pipe (it's important that the pipe is only in the tank during feeding time, otherwise another fish may claim it). Every week or so push the food a little further into the pipe so after a month or so he's all the way in the pipe far enough that he can't escape in half a second. Then simply net either end of the pipe very gently (you don't want to startle him and let him get away) and pull him and the pipe out.
You have to do this as gradually as possible because he has to associate the pipe with food AND be comfortable entering it and staying in there for a minute or more.