Perhaps Math::Vector? It'd still do the addition correctly without a third dimension.

Though, it's really just:

my $a1 = [1,2]; bless $a1, "test";
my $a2 = [2,4];
my $a3 = $a1+$a2;

print "@$a3\n";

package test;

use strict; 
use overload '+' => 
    sub { bless [ $_[0][0]+$_[1][0], $_[0][1]+$_[1][1] ], ref $_[0] };

# NOTE: I'm ignoring an important third argument that you'd need to ch
+eck
# if you wanted to support subtraction

1;
[download]

UPDATE: I didn't notice that moritz wrote basically the exact same thing as the above, sorry. I'm leaving it because it's a slightly different style.