Extending Cucumber `World` for Chimp tests

According to the Cucumber-js documentation, utilities should be made available by creating a constructor function called World. In Chimp, this constructor already exists, creating a world loaded with utility.

How do I extend this constructor to add my own utilities?

I tried:

function sayHi() {
  console.log('Hi!');
}

module.exports = function() {
  var ChimpWorld = this.World;
  this.World = function() {
    this.sayHi = sayHi;
    ChimpWorld.call(this);
  }
};

Which results in:

/Users/thomasvanlankveld/.nvm/v0.12.4/lib/node_modules/chimp/node_modules/fibers/future.js:267
                    throw(ex);
                          ^
TypeError: undefined is not a function
  at [object Object].World (/Users/thomasvanlankveld/.nvm/v0.12.4/lib/node_modules/chimp/lib/cucumberjs/world.js:21:7)
  at new World (/Users/thomasvanlankveld/Sites/my-app/tests/features/world.js:9:16)
  at Array.<anonymous> (/Users/thomasvanlankveld/.nvm/v0.12.4/lib/node_modules/chimp/lib/cucumberjs/cucumber-wrapper.js:137:24)
  at Object.Future.return (/Users/thomasvanlankveld/.nvm/v0.12.4/lib/node_modules/chimp/node_modules/fibers/future.js:262:13)
  at Object.<anonymous> (/Users/thomasvanlankveld/.nvm/v0.12.4/lib/node_modules/chimp/node_modules/fibers/future.js:336:16)
  at /Users/thomasvanlankveld/.nvm/v0.12.4/lib/node_modules/chimp/node_modules/underscore/underscore.js:890:21
  at /Users/thomasvanlankveld/.nvm/v0.12.4/lib/node_modules/chimp/lib/cucumberjs/cucumber-wrapper.js:127:19

So it seems Chimp's World constructor is not available to me.

In case this is not possible, is there another way to make my own helpers available across files?