thekestrel,
Here is how I would do it:

#!/usr/bin/perl
use strict;
use warnings;

my @uniq;
my $add = uniq_array( \@uniq );
$add->(3,1,4,1,5,9);
$add->(2,7,2,7,2,7);
print "$_\n" for @uniq;

sub uniq_array {
    my ($aref, %uniq) = shift();
    return sub { push @$aref, grep { ! $uniq{$_}++ } @_ };
}
[download]

Let me know if you have any questions.

Update: Over 2 months after posting this, Roy Johnson asked why I used map instead of grep inside the return sub. The answer is that I was modifying a piece of existing code that does much more. For the sake of clarity, I have replaced the funny looking map.