Snippets from my post on creating dynamic/configurable builds with Grunt and Closure Compiler.

closure-compiler-config-2.js

//configure closure compiler
var closureFiles = handlerClassNames.map(function (name) {
  return 'src/' + name + '.js';
});
closureFiles.unshift('src/InputController.js');
closureFiles.push('build/bundle.js');
/* ... */
grunt.config.set('closure-compiler.bundle', {
  closurePath: 'lib/closure',
  jsOutputFile: 'build/input-controller.js',
  js: closureFiles,
  maxBuffer: 500,
  options: closureOptions
});
grunt.task.run('closure-compiler:bundle');

closure-compiler-config.js

'closure-compiler': {
  all: {
    closurePath: 'lib/closure',
    jsOutputFile: 'build/build.js',
    js: ['src/*.js'],
    maxBuffer: 500,
    options: {
      'language_in': 'ECMASCRIPT5_STRICT',
      'process_common_js_modules': null,
      'transform_amd_modules': null,
      'common_js_entry_module': '???'
    }
  }
}

configure-wrap-task.js

// task configuration:
wrap: {
  'all': {
    src: ['build/input-controller.js'],
    dest: './',
    wrapper: [
      UMDWrapper.before.join(''),
      UMDWrapper.after.join('')
    ]
  }
}
/* ... */
// later, as a last step of the configure task:
grunt.task.run('wrap:all');

entry-point.js

// create bundle file contents
var bundleFileContents = [
  '/*global define:false*/',
  '/*jshint indent:false*/',
  'define([',
  '"../src/InputController",',
  handlerModuleNames.join(',\n'),
  '], function (InputController, ' + handlerClassNames.join(', ') + ') {',
  '"use strict";',
  'var bundle = new InputController();',
  'bundle.registerDeviceHandlers([' + handlerClassNames.join(', ') + ']);',
  'return bundle;',
  '});\n'
].join('\n').replace(/"/g, '\'');

// write to disk
grunt.file.write('build/bundle.js', bundleFileContents);

gathering-names.js

grunt.registerTask('configure', 'A task to configure specific handlers', function () {

  var handlerClassNames = [].slice.call(arguments).map(function (name) {
    return name.slice(0, 1).toUpperCase() + name.slice(1, name.length) + 'Handler';
  });
  var handlerModuleNames = handlerClassNames.map(function (name) {
    return '"../src/' + name + '"';
  });

  /* ... */
}

grunt-option.js

var handlers = grunt.option('handlers') || ('mouse,keyboard,gamepad,speech');
grunt.registerTask('default', ['configure:' + handlers.replace(/,/g, ':')]);

umd-wrapper.js

// define wrapper code
var exportName = 'inputController';
var UMDWrapper = {
  before: [
    '(function (name, definition, global) {',
    'if (typeof define === "function") {',
    'define(definition);',
    '} else if (typeof module !== "undefined" && module.exports) {',
    'module.exports = definition();',
    '} else {',
    'global[name] = definition();',
    '}',
    '})("' + exportName + '", function () {'
  ],
  after: [
    'return module$build$bundle; ',
    '}, this);\n'
  ]
};