config.ru

require 'sj'

run SinatraJekyll

sj.rb

require 'sinatra/base'

class SinatraJekyll < Sinatra::Base
  
  get /.+/ do
    send_sinatra_file(request.path) {404}
  end

  not_found do
    send_sinatra_file('404.html') {"Sorry, I cannot find #{request.path}"}
  end

  def send_sinatra_file(path, &missing_file_block)
    file_path = File.join(File.dirname(__FILE__), '_site',  path)
    file_path = File.join(file_path, 'index.html') unless file_path =~ /\.[a-z]+$/i  
    File.exist?(file_path) ? send_file(file_path) : missing_file_block.call
  end

end