Usergroups that can't be ignored besides Admin/Mod?

[cirdok2]

Hi,
using the ignore system, Admin/Moderators can't be ignored.

How can I set more usergroups as a "cannot be ignored usergoup", so if a user is trying to ignore them he will not be able to do that?

Should be somewhere something like:

"if usergroup(admin) or usergroup(mod) then you can't add it".

Once found it, it should be easy to add other usergroups (adding all of them would be also a good workaround to disable this system).
I don't need an option/switch/usergroup setting, I would be more than happy modifying manually the conditional)

But I don't know which templates/files are involved.
Anyone can help? Any hint?

Thank you!