Check out Tie::TwoLevelHash. I think it tries to achieve exactly what you want.

use Tie::TwoLevelHash;
use strict;
use warnings;
my $hash;
my $file = "datafile";
tie (%hash, 'Tie::TwoLevelHash', $file, 'rw'); 
$hash{PEOPLE} = {YOU => "me"};
$hash{PEOPLE} = {WHO => "cares"};
$hash{PEOPLE} = {WHO => "works"};
$hash{ME} = { I => "See"};
__DATA__
ME
    I: See

PEOPLE
    WHO: works
    YOU: me
[download]

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