pry_client.rb

require 'pry'
require 'drb'

DRb.start_service
client = DRbObject.new nil, ARGV[0]

# Dummy proxy, DRb won't allow us to pass Readline directly.

Proxy = Object.new

def Proxy.readline(prompt)
  Readline.readline(prompt)
end

client.input  = Proxy
client.output = $stdout

DRb.thread.join

pry_server.rb

require 'pry'
require 'drb'

Client = Struct.new(:input, :output)

class Object
  def remote_pry
    client = Client.new(nil, nil)

    DRb.start_service "druby://localhost:5000", client
    puts "NOTE: The DRb server is #{DRb.uri}"

    # Just loop until we get our client
    until client.input && client.output
      sleep 0.01 # avoid busy loop
    end

    input  = client.input
    output = client.output

    # Ensures arity of readline is set to one.
    proxy = Object.new
    proxy.define_singleton_method :readline do |prompt|
      input.readline(prompt)
    end

    Pry.start(self, :input => proxy, :output => output)

    DRb.stop_service
  end
end

class Foo
  def initialize(x, y)
    binding.remote_pry
  end
end

Foo.new(0, 50)