How to configure the rootURL?

I'd like to host an Ember app in the /blog/ directory. I found the following code in the documentation to make that happen but I have trouble to make it work.

App.Router.reopen({
  rootURL: '/blog/'
});

At what position do I have to include this code or is there a better way to do it anyway? I'd like to fire up ember build --environment=production and than copy /dist/* to the /blog/ directory on the webserver.