Route 53 - Special domain for a single page on existing server

I have a complex web app at example-app.com, hosting fully on AWS using ELB and Route 53 for DNS. It's a Rails app.

I'm running an experiment that I'm using in the rails app, at example-app.com/test. I want to set up new-domain-app.com, to point at example-app.com/test, and have the URL cloacked to always be new-domain-app.com. It's a single page site, so it shouldn't require any navigation.

I'm having a lot of trouble figuring out how to set up my DNS on Route 53 to accomplish this. Does anyone have good ideas on what this Route 53 configuration should look like?