trying to add fake extension to activemerchant to allow conditionally requiring nokogiri based on ruby version at gem install time

activemerchant.gemspec.diff

index 652e40c..233d9df 100644
--- a/activemerchant.gemspec
+++ b/activemerchant.gemspec
@@ -13,8 +13,8 @@ Gem::Specification.new do |s|
   s.homepage = 'http://activemerchant.org/'
   s.rubyforge_project = 'activemerchant'
 
-  s.files = Dir['CHANGELOG', 'README.md', 'MIT-LICENSE', 'CONTRIBUTORS', 'gem-public_cert.pem', 'lib/**/*', 'vendor/**/*']
-  s.require_path = 'lib'
+  s.files = Dir['CHANGELOG', 'README.md', 'MIT-LICENSE', 'CONTRIBUTORS', 'gem-public_cert.pem', 'lib/**/*', 'vendor/**/*', 'ext/nokogiri_conf.rb']
+  s.require_paths = ['lib', 'ext']
 
   s.has_rdoc = true if Gem::VERSION < '1.7.0'
 
@@ -24,7 +24,7 @@ Gem::Specification.new do |s|
   s.add_dependency('builder', '>= 2.0.0')
   s.add_dependency('json', '>= 1.5.1')
   s.add_dependency('active_utils', '>= 1.0.2')
-  s.add_dependency('nokogiri', "< 1.6.0")
+  s.extensions = ['ext/nokogiri_conf.rb']
 
   s.add_development_dependency('rake')
   s.add_development_dependency('mocha', '~> 0.13.0')

nokogiri_conf.rb

require 'rubygems'
require 'rubygems/command.rb'
require 'rubygems/dependency_installer.rb'
begin
  Gem::Command.build_args = ARGV
  rescue NoMethodError
end
inst = Gem::DependencyInstaller.new
begin
  if RUBY_VERSION < "1.9"
    inst.install "nokogiri", "< 0.6.0"
  else
    inst.install "nokogiri", "~> 0.6.0"
  end
  rescue
    exit(1)
end

f = File.open(File.join(File.dirname(__FILE__), "Rakefile"), "w")   # create dummy rakefile to indicate success
f.write("task :default\n")
f.close

output.txt

$ gem build activemerchant.gemspec && gem install ./activemerchant-1.35.1.gem 
WARNING:  licenses is empty
  Successfully built RubyGem
  Name: activemerchant
  Version: 1.35.1
  File: activemerchant-1.35.1.gem
Building native extensions.  This could take a while...
ERROR:  Error installing ./activemerchant-1.35.1.gem:
	ERROR: Failed to build gem native extension.

    No builder for extension 'ext/nokogiri_conf.rb'

Gem files will remain installed in $MY_GEMS_DIR/activemerchant-1.35.1 for inspection.
Results logged to $MY_GEMS_DIR/activemerchant-1.35.1/ext/gem_make.out