Preference file question

I am working in the preference file trying to establish a standard preference file so all the users see the same thing and our illustrations all look the same. What I would like to do is add a separator line in the preference file. Example if you look at the Pens dialog box you see the separator line below "Center line". I would like to add other separator lies to break up groups but I do not see where these are generated in the preference file. Does anyone how to generate these?

Thanks,

Keith Howard