Here's an updated form of my code example from that discussion:

use strict;

sub nested_value {
  my $href = shift;
  my $keys = shift;

  my $last_key = pop @$keys;

  for my $key (@$keys) {
    $href = $href->{$key} ||= {};
  }

  if (@_) {
    $href->{$last_key} = shift;
  }

  return $href->{$last_key};
}

my %hash;

nested_value(\%hash, [qw/one two three/], 1);
print nested_value(\%hash, [qw/one two three/]), "\n";

use Data::Dumper;

print Dumper \%hash;
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Note that this code assumes that each key will either point to a hash reference or to a value. If you set a value first, and then try to use it as a nested hash, you'll get an error from use strict. If you set a nested hash first, and then set a value at the same level, you'll delete the entire nested hash. Error checking could be added to the sub to handle those situations gracefully.

Adapted from (tye)Re: varying length multi-dimensional hashes:

sub setHoH {
    my( $hashref, $val, @keys )= @_;
    my $ref= \$hashref;
    for(  @keys  ) {
        $ref= \$$ref->{$_};
    }
    $$ref= $val;
}
@array= qw/one two three/;
setHoh( \%hash, 1, @array );
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Why not use an empty hash (ie {}) as your default true value? Then when $hash{69}{15} is set to {}, there is no problem setting $hash{69}{15}{14}{13} to {} after that.

Well hot-dog!
Thank you. I was thinking way to hard about that one for such a simple answer.

Why don't you just use $hash{join $;, @list}= 1 instead?

        - tye (but my friends call me "Tye")

Because that would produce:
$hash{onetwothree} = 1
instead of
$hash{one}{two}{three} = 1