Use your finger, I know it sounds crude and certainly breaks the accepted rules that you don't touch the neg with bare fingers or place anything on the emulsion side, but it has always worked for me. I've had a look at the image posted in the gallery and the scratch does not seem too obvious and although it can be seen it looks like a scuff mark on the playground.

One little tip about re-touching scratches, break the area into sections by spotting along the scratch leaving gaps. Don't try to start at one end and finish at the other you will end up with a dark halo along the length of the scratch.