Custom grunt directive processing in config?

grunt.js

module.exports = function (grunt) {
  // custom helper
  grunt.registerHelper('concat_two_strings', function (a,b) {
    return a + b;
  }

  // config
  grunt.initConfig({
    lint: { files: ['<concat_two_strings:need:linting>/*.js'] } // is this supposed to work or not?
  });
};

The entire string has to be a directive to be valid, so this could work: '<concat_two_strings:need:linting/*.js>'

oh ok thanks!