通过使用 mysql2 gem，我能够在没有 fork 的情况下使其工作

I was able to get this to work without a fork by using the mysql2 gem

require 'rubygems'
require 'active_record'
require 'mysql2'
require 'net/ssh/gateway'

gateway = Net::SSH::Gateway.new(
  'remotehost.com',
  'username'
)
port = gateway.open('127.0.0.1', 3306, 3307)

class Company < ActiveRecord::Base
  establish_connection(
    :adapter  => "mysql2",
    :host     => "127.0.0.1",
    :username => "dbuser",
    :password => "dbpass",
    :database => "dbname",
    :port     => 3307
  )
end
puts Company.all.size