Walk up project tree to resolve project (ext) properties in Gradle

gistfile1.txt

//root build.gradle
ext {
  javaVersion = JavaVersion.VERSION_1_7
}
 
Project.metaClass.prop { name ->
  delegate.with {
    ext.properties.containsKey( name ) ?
        ext.properties[ name ] : parent?.prop( name )
  }
}
 
//:subproject1 build.gradle
sourceCompatibility = prop("javaVersion")

I wish gradle :properties had a recursive option to automate this.