use Sys::Export::CPIO;
  use Sys::Export -src => '/', -dst => Sys::Export::CPIO->new("initrd.cpio");
  
  rewrite_path '/sbin'     => '/bin';
  rewrite_path '/usr/sbin' => '/bin';
  rewrite_path '/usr/bin'  => '/bin';
  
  add '/bin/busybox';
  add ...;
  finish;