[ruby-core:30175] [Problem] DATA and __END__ in a loaded rb file

how to get global constant DATA in file <a.rb>,if a.rb is loaded by b.rb.
when b.rb is exec by Ruby,even if the DATA is used in a.rb,infact the DATA
is from b.rb,
because a.rb is loaded by b.rb.

how to resolve it?

such as:

<b.rb> :

Cui$ cat /usr/local/ruby-1.8.7-p160/bin/roadrunner
#!/usr/local/ruby-1.8.7-p160/bin/ruby
#
# This file was generated by RubyGems.
#
# The application 'roadrunner' is installed as part of a gem, and
# this file is here to facilitate running it.
#

require 'rubygems'

version = ">= 0"

if ARGV.first =~ /^_(.*)_$/ and Gem::Version.correct? $1 then
  version = $1
  ARGV.shift
end

gem 'roadrunner', version
load Gem.bin_path('roadrunner', 'roadrunner', version)

<a.rb>
#this is code

__END__
#!/usr/bin/env ruby
#main.rb
#this is the DATA