Conditionally disable the proxy forwarding by https://github.com/dblock/heroku-forward using the DISABLE_FORWARD_PROXY environment setting.

config.ru

require 'rubygems'
require 'bundler'

if ENV['DISABLE_FORWARD_PROXY']

  eval File.read(::File.expand_path('../my_app.ru',  __FILE__))

else

  $stdout.sync = true
  Bundler.require(:rack)
  
  port = (ARGV.first || ENV['PORT'] || 3000).to_i
  env = ENV['RACK_ENV'] || 'development'

  require 'em-proxy'
  require 'logger'
  require 'heroku-forward'

  #
  # Setup a reverse proxy for faster Heroku boot and future load-balancing.
  #

  application = File.expand_path('../my_app.ru', __FILE__)
  backend = Heroku::Forward::Backends::Thin.new(application: application, env: env)
  proxy = Heroku::Forward::Proxy::Server.new(backend, { host: '0.0.0.0', port: port })
  proxy.logger = Logger.new(STDOUT)
  proxy.forward!

end