Gradle: how do I configure the jar location to be in the parent directory of the project?

Gradle: how do I configure the jar location to be in the parent directory
of the project?

I'm trying to build a Gradle JAR project that is a subproject of another
and would like the output JAR file to be in a parent directory (to be
specific in the "lib" directory of the parent, or sibling). How do I
configure Gradle for this and where is this documented?