A while ago I whipped up Tie::Subset::Hash, and I took this oppertunity (and the inspiration from Discipulus's node) to expand upon that with Tie::Subset::Hash::Masked:

use Data::Dumper;
use Tie::Subset::Hash::Masked;

my @unwanted = qw/ schema log /;
my %hash = ( schema=>1, log=>2, aa=>3 );
tie my %masked, 'Tie::Subset::Hash::Masked', \%hash, \@unwanted;
print Dumper(\%masked);

__END__
$VAR1 = {
          'aa' => 3
        };
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