sub doubleStack
{
    my $count = pop;
    my @out;
    while (@_){push @out, [splice @_,0,$count];}
    return @out;

}

##</code><code>##

doubleStack(qw(a b c e 1 2 3 4 5 3 f),3)

returns:
$VAR1 = [
          [ 'a', 'b', 'c' ],
          [ 'e', '1', '2' ],
          [ '3', '4', '5' ],
          [ '3', 'f']
        ];