--- ./setup.rb-org	2008-05-14 23:21:09.000000000 +0900
+++ ./setup.rb	2008-05-16 07:25:24.000000000 +0900
@@ -97,6 +97,11 @@
     lib_dir = File.join prefix, 'lib'
     bin_dir = File.join prefix, 'bin'
 
+    if ARGV.grep(/^--tmppath/) then
+      lib_dir = File.join prefix, Gem::ConfigMap[:sitelibdir]
+      bin_dir = File.join prefix, Gem::ConfigMap[:bindir]
+    end
+
     mkdir_p lib_dir
     mkdir_p bin_dir
   end