Dynamically loading tasks from useminPrepare

// Gruntfile.js
'use strict';

var path = require('path');

module.exports = function (grunt) {

    // Load externally-defined tasks
    grunt.loadTasks('tasks/grunt');

    // Load grunt tasks automatically
    require('load-grunt-config')(grunt, {
        configPath: path.join(process.cwd(), 'tasks/grunt/options'),
        init: true,
        config: {
            config: {
                app: 'app',
                dist: 'dist',
                tmp: '.tmp',
                test: 'test'
            }
        },
        loadGruntTasks: {
            pattern: 'grunt-*'
        }
    });

    // Time how long tasks take. Can help when optimizing build times
    require('time-grunt')(grunt);
};



// tasks/grunt/options/useminPrepare.js:
module.exports = {
    // Reads HTML for usemin blocks to enable smart builds that automatically
    // concat, minify and revision files. Creates configurations in memory so
    // additional tasks can operate on them
    options: {
        dest: '<%= config.dist %>'
    },
    html: '<%= config.app %>/index.html'
};

// tasks/grunt/options/usemin.js:
module.exports = {
    // Performs rewrites based on rev and the useminPrepare configuration
    options: {
        assetsDirs: ['<%= config.dist %>', '<%= config.dist %>/images']
    },
    html: ['<%= config.dist %>/{,*/}*.html']
};


// here is my build task.  useminPrepare is included in 'concurrent:dist'
module.exports = function(grunt) {
    grunt.registerTask('build', [
        'clean:dist',
        'includereplace',
        'jshint',
        'modernizr',
        'concurrent:dist',
        'copy',
        'concat',
        'uglify',
        'usemin'
    ]);
};



/* The preceding configuration gives me the correct useminPrepare output:

    Running "useminPrepare:html" (useminPrepare) task
    Going through app/index.html to update the config
    Looking for build script HTML comment blocks

    Configuration is now:

      concat:
      { files:
       { '.tmp/concat/scripts/head-scripts.js': [ 'app/scripts/vendor/modernizr.js' ],
         '.tmp/concat/scripts/app-prod.js':
          [ 'app/scripts/main.js',
            'app/scripts/app.js' ] },
      generated:
       { files:
          [ { dest: '.tmp/concat/scripts/head-scripts.js',
              src: [ 'app/scripts/vendor/modernizr.js' ] },
            { dest: '.tmp/concat/scripts/app-prod.js',
              src:
               [ 'app/scripts/main.js',
                 'app/scripts/app.js' ] } ] } }

      uglify:
      { files:
       { '<%= config.dist %>/concat/scripts/head-scripts.js': [ '.tmp/concat/scripts/head-scripts.js' ],
         '<%= config.dist %>/concat/scripts/app-prod.js': [ '.tmp/scripts/app-prod.js' ] },
      generated:
       { files:
          [ { dest: 'dist/scripts/head-scripts.js',
              src: [ '.tmp/concat/scripts/head-scripts.js' ] },
            { dest: 'dist/scripts/app-prod.js',
              src: [ '.tmp/concat/scripts/app-prod.js' ] } ] } }

  
  However, grunt build will not complete because it no concat targets are found (nor uglify targets, for that matter).
  If it were working properly, the concat:generated and uglify:generated tasks would have been added to the loaded grunt tasks, which would then be executed by usemin in the last step of my build.
  
  Hopefully this is all clear!
*/