The work is done inside of lib.pm's import method, so you might try:

BEGIN {
  use Sys::Hostname;
  require lib;
  if (hostname() eq 'foo.bar.org') {
    lib->import('/alternate/libdir');
  } else {
    lib->import('/default/libdir');
  }
}
[download]

The advantage of this over the unshift trick is that you'll get architecture-dependent paths added, as well.

perl -pe '"I lo*`+$^X$\"$]!$/"=~m%(.*)%s;$_=$1;y^`+*^e v^#$&V"+@( NO CARRIER'