I have attached a simple mod that will allow you to specify which usergroups have access to the ignore system. Anyone not belonging to one of these groups will not see the link on user profiles to add to ignore list, nor will they see the link in their UserCP to edit their ignore list.
If a user without permission tries to circumvent the system by manually entering a URL to add users to their ignore list, they will get a "no permission" error.
Once you install the product, visit the settings to enable the product, and select your usergroups.
Please give this a try and let me know if you'd like anything added.