Emberjs 1.12.1 - how to register a helper without using export default

I am not using ember-cli (long story) and have defined

/helpers/format-date.js

with contents:

Ember.Handlebars.makeBoundHelper('format-date', function(value) {
  return <my code>;
}

I have tried:

Ember.Handlebars.registerHelper
Ember.Handlebars.registerBoundHelper
Ember.Handlebars.makeThisBloodyHelperRegister

I have also tried to put at the start of the line:

App.ApplicationHelper = Ember.Handlebars...
App.FormatDateHelper = Ember.Handlerbars...

and various other styles. Nothing works, it always complains it cannot find the helper.

The project I am using can NOT use export default, there is no transpiler being used.