You CAN inherit from a Rails::Application child!

gistfile1.rb

class Settings < YourAppName::Application
end

# The Problem:
# ==> .../.rvm/gems/ruby-1.9.3-p125/gems/railties-3.2.2/lib/rails/railtie/configurable.rb:12:in `inherited': 
# You cannot inherit from a Rails::Application child (RuntimeError)

# Because:
# http://apidock.com/rails/Rails/Application/Configurable/ClassMethods/inherited

# Resolving:

class << YourAppName::Application
  def inherited(base)
  end
end

class Settings < YourAppName::Application
  # your code here...
end

# :D