If you want to place personalized ignore messages in the chatrooms you can do what I do now.

Open up your large event viewer by clicking on your console icon and leave it minimized for convenience.

Then when you ignore someone, go to your event logger and right click and copy the ignore entry for that person, paste it in your message box, then type your own personalized message for that individual behind it.

A little more involved than a automatic message but then again you can personalize the message for each individual that you ignore.