Yeah I figured that would be a problem. Looking around I think you should try moving the APP_CONFIG setup into application.rb. This will then take place before the the environments/* files.  There might be an issue when  There is this SO which mentions this:
http://stackoverflow.com/questions/6932346/understanding-rails-configuration
This blog post also loads a config in application.rb:
http://grosser.it/2012/03/03/moving-config-mess-from-environment-files-to-config-yml/
And this this code from a rails cast does something similar:
https://github.com/railscasts/085-yaml-configuration-revised/blob/master/blog-after/config/application.rb

So I think this approach is pretty standard now.