I clicked the link you provided and didn't get much info out of it at all. Let alone enough to configure it.
So I took some of the code you wrote up there and was able to get this working. However, I could only get it to work at the global level, which is good enough for now. I was unable to get a custom message to display for those who hit blacklisted sites. I'm also wondering if there's a way to schedule when these black lists will occur. It doesn't seem that way. For example, I'd like to block some sites during work hours and other sites during evening hours. The sites should be available at all other times.