gistfile1.rb

#in controller
key = store_params(hash_of_params_to_keep)

redirect_to some_path(:params_key => key)

-----------

def store_params(hash_of_params)
  key = Time.now.to_s + rand(10000).to_s #or some other unique key
  session[:stored_params] ||= {}
  session[:stored_params][key] = hash_of_params
  key
end

--------------
#in application_controller
before_filter :restore_params_by_key

def restore_params_by_key
  params.merge!(session[:stored_params][params[:params_key]]) if session[:stored_params] and params[:params_key]
end