Looks like there is no such custom plugin, and even there is one, it’s not so straightforward to integrate it as we rely on stylelint to detect used CSS syntax. Unfortunately as of today CSS analyzer is not our priority so we don’t have bandwidth to take care of JSF EL. Moreover I’m not sure this feature is required for many users.
One workaround for you could be to execute the script which removes EL from your files before analysis (of course without commiting those changes).
Sorry for not being able to provide anything better