Do it backwards.

use strict;
use warnings;
use Data::Dumper;

my @foo = qw/1 2 3 4 5 6/;
my $href;

foreach my $key ( reverse @foo ) {
    $href = { $key, $href };
}

print Dumper $href;
[download]

This also turns out to be very similar to one of the easiest ways in Perl to build a traditional ( in the tradition of computer science ) linked list.