Adding a classpath entry outside gradle classpath container

Hello, is there a possibility to add a new classpath entry outside of the gradle classpath container using eclipse.classpath.file.whenMerged? It seems I can only do this via eclipse.classpath.file.withXml, but that that does nothing on ‘Refresh Gradle Project’, only when calling eclipseClasspath task directly, which is a dealbreaker.
It may seem as a weird request, but I want to do this as a workaround for

Alternate question - is there any way for me to make Buildship take into account what’s defined in eclipse.classpath.file.withXml when generating .classpath?