Simplest way to take an Ember application down for maintenance

I have an Ember.js application being served from S3, uploaded using ember-cli-deploy. It has a Rails backend that I take down for maintenance from time to time. During this time I would like my ember application to redirect every route to an "undergoing maintenance" page.

Can I do this within the Ember framework, or am I better off temporarily replacing index.html on S3 with a static file?