How to mute a 3rd party librarie's overly verbose WARN logger?

This is related to Configure logging for 3rd party libs in a plugin but since that topic is closed, I’d like to re-engage the discussion.

We’re using apache fop for some xslt processing. That beast spits out a ton of WARN messages that can (must in fact) be ignored, but that pollute the whole build log considerably.

Before gradle 2.4, we used some nasty code to raise the level of just the org.apache.fop logger to ERROR, but since Gradle 2.4, that doesn’t seem to work anymore - looks like some internal stuff around logging got changed… anyway.

We’d really need a way to tell that logger to be quiet, but without impacting the rest of the build like with the --quiet flag.