sudoers for passwordless sudoedit, except for sudoers

I want to configure passwordless sudoedit, to edit files under /etc with the exception of sudoers files themselves. I tried using the following /etc/sudoers.d/sudoedit:

%sudo ALL=(root) NOPASSWD: sudoedit ^/etc/(?!sudo).*$

but that does not seem to work as sudo uses an old regex engine without the negative lookahead feature. Is there another way to achieve this? Maybe with the combination of /etc and the negation of !/etc/sudo?