How can I copy Scala.js source maps using resourceGenerators?

I'm using resourceGenerators sbt key to copy fastOptJs-generated .js files when using products, like this:

(resourceGenerators in Compile) <+=
        (fastOptJS in Compile in frontend, packageScalaJSLauncher in Compile in frontend, packageJSDependencies in Compile in frontend)
          .map((f1, f2, f3) => {
            Seq(f1.data, f2.data, f3)
          })

Running the following in sbt, I can see the path of generated file:

> show frontend/fastOptJS
[info] Attributed(/some/path/frontend/target/scala-2.11/frontend-fastopt.js)
[success] Total time: 0 s, completed Mar 12, 2016 1:59:22 PM

Similarly, I can easily see where Scala.js-generated launcher ends up:

> show frontend/packageScalaJSLauncher
[info] Attributed(/some/path/frontend/target/scala-2.11/frontend-launcher.js)
[success] Total time: 0 s, completed Mar 12, 2016 2:00:10 PM

I cannot, however, find a task/key that would point me to location of .js.map file. I tried looking in the plugin sources, but couldn't find it. Is there any way of doing that without resorting to creating a manual mapping in build.sbt?