for (sort by_seq([qw(five nine one seven three)]), keys %h) {

##</code><code>##

use strict;
#use diagnostics;

sub by_seq { 
    my $seq_aref = shift;
    my %seq_helper; 
    { 
        my $index = 0; 
        for my $item (@{ $seq_aref }) { 
           $seq_helper{$item} = $index; $index++;
        };
    };

    # Here I return a subroutine that takes two arguments
    # (the left and the right element to be compared)
    return sub { $seq_helper{$_[0]} <=> $seq_helper{$_[1]} };
}; 

# -- 

my %h = (one=>2,three=>4,five=>6,seven=>8,nine=>0);

# Create our custom comparison routine
my $sorter = by_seq([qw(five nine one seven three)]);

for (sort {$sorter->($a,$b)}, keys %h) {
    print "$_: $h{$_}\n";
};