Heroku Promotion issue with and Rails/JS app and ENV variables

I have an issue very similar to this: Using runtime env with React and heroku

My JS file that retrieves the ENV variables ends up hard-coded. When I promote from Staging to Production, the staging vars remain.

My setup is:

• Rails 3 backend
• AngularJS frontend (we're re-platforming this year)
• rails-environment.js.erb ( file that reads ENV[varname] and stores in JS vars

Honorable mentions: Rails Env Issue