You can untaint $Bin in a BEGIN block.

#!/usr/bin/perl -T

use warnings;
use strict;

use FindBin qw/$Bin/;
BEGIN {
  if ($Bin =~ m!([\w\./]+)!) {
    $Bin = $1;
  } else {
    die "Bad directory $Bin\n";
  }
}
use lib "$Bin/../lib";

use Data::Dumper;

print "Hello!!\n";
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