Optimizing JS from WebJars using sbt-rjs in a Play 2.3.x app

Is it possible to have a Play 2.3 app concat/optimize JS (using sbt-rjs) that's included in my app via WebJars?
To give a concrete example: I'm trying to create a core.js module which contains all my 3rd party libraries concatenated and minified in a single file which can then be specified as a dependency for other AMD modules.
It would be great to include these libraries via WebJars instead of downloading the source "manually".

Here's a snippet from my build.sbt file where I'm specifying my webjar dependencies:

// Webjars
libraryDependencies ++= Seq(
  "org.webjars" % "requirejs" % "2.1.15",
  "org.webjars" % "underscorejs" % "1.7.0",
  "org.webjars" % "jquery" % "1.11.1",
  "org.webjars" % "bootstrap" % "3.3.1" exclude("org.webjars", "jquery"),
  "org.webjars" % "angularjs" % "1.3.4-1" exclude("org.webjars", "jquery")
)

Here's my requireJS build config

requirejs.config({
  baseUrl: '/assets/javascripts',
  shim: {
    'jsRoutes': {
      deps: [],
      exports: 'jsRoutes'
    },
    'angular': {
      deps: ['jquery'],
      exports: 'angular'
    },
    'underscore': {
      exports: '_'
    },
    'angularRoute': ['angular'],
    'angularCookies': ['angular'],
    'bootstrap': ['jquery']
  },
  paths: {
    'requirejs': '../lib/requirejs/require',
    'jquery': '../lib/jquery/jquery',
    'underscore': '../lib/underscorejs/underscore',
    'angular': '../lib/angularjs/angular',
    'angularRoute': '../lib/angularjs/angular-route',
    'angularCookies': '../lib/angularjs/angular-cookies',
    'bootstrap': '../lib/bootstrap/js/bootstrap',
    'jsRoutes': '/jsroutes',
    'core': './core'
  },
  modules: [
    {
      name: 'core'
    }
  ]
});

And finally, here's my core.js module:

define(['angular', 'angularRoute', 'underscore', 'bootstrap'], function() {
  // core dependencies are loaded...
});

After running activator clean stage from the command line I was hoping the built core.js file would include all my specified dependencies concatenated and minified into a single file, but it doesn't include any of them. If I specify a non-WebJar file as a dependency for core.js, it does optimize that correctly.

Is what I'm trying to do possible? I've been googling quite a bit and haven't been able to find a clear answer either way.

Thanks!

I am using Play 2.4.3.

Added addSbtPlugin("com.typesafe.sbt" % "sbt-rjs" % "1.0.7") to plugins.sbt

// rjs = RequireJS, uglifies, shrinks to one file, replaces WebJars with CDN
client accepts them
pipelineStages := Seq(rjs, digest, gzip)

This in my build.sbt does all the shrinking work etc. to bower JS, and webjars.