Gradle: is it possible to publish to Gradle's own local cache?

Note that the local Maven repository is not (really) a cache, and that the Gradle cache is not a repository. Gradle uses its cache only to cache remote artifacts, it should not copy artifacts retrieved from local Maven repositories there. In turn, you cannot publish artifacts to the Gradle cache.

So the approach to publish to and use mavenLocal() should not be as wasteful as you think. Also, you do not have to add mavenLocal() to all projects of a multi-project separately. You can simply use something like allprojects { repositories { mavenLocal() } } in your root project. Or if you want mavenLocal() in all your independent Gradle projects you could even try adding it to ~/.gradle/init.gradle.