perl -MConfig -e 'print $Config{usesitecustomize} ? "yes, edit $Config{sitelib}/sitecustomize.pl" : "no luck", "\n"'
 

##</code><code>##

  use lib qw(/my/preferred/dir);
  print "SITECUSTOMIZE: INC: @INC\n" if $ENV{DEBUG_SITECUSTOMIZE}; # just for fun