As a matter of fact there is no need to for you to create inner hash if you don't need it RIGHT AT THE MOMENT. it will be created at the time you want it. For example:

use Data::Dumper;

use strict;
use warnings;

my $h = {};
$h->{"a"}{"b"}{"c"} = 1;
print Dumper($h);
[download]

This works, and there is no need to create level a first, then level b, then assign level c. Level a and b magically come to existance.