flash_session_cookie_middleware.rb

# put this in app/middleware
# make sure to add app/middleware to your config.load_paths in environment.rb

# add this to your session_store.rb in config/initializers

# ActionController::Dispatcher.middleware.insert_before(
#  ActionController::Session::CookieStore, 
#  FlashSessionCookieMiddleware, 
#  ActionController::Base.session_options[:key]
# )

require 'rack/utils'

class FlashSessionCookieMiddleware
  def initialize(app, session_key = '_session_id')
    @app = app
    @session_key = session_key
  end

  def call(env)
    if env['HTTP_USER_AGENT'] =~ /^(Adobe|Shockwave) Flash/
      params = ::Rack::Utils.parse_query(env['QUERY_STRING'])
      
      unless params[@session_key].nil?
        env['HTTP_COOKIE'] = "#{@session_key}=#{params[@session_key]}".freeze
      end
    end
    
    @app.call(env)
  end
end