Select a font that includes the ½ symbol, then include the PostScript escape code for that symbol (275 in the normal encoding). The escape codes are defined in the PostScript Language Reference Manual Appendix E

#!/usr/bin/perl

use warnings;
use strict;
use PostScript::Simple;

my $p = new PostScript::Simple(papersize => "A4",
                                colour => 1,
                                eps => 0,
                                units => "in");

$p->setcolour("black");
$p->setfont("Times-Roman-iso", 20);
$p->text(1,1, "Chee\275se");
$p->output("file.ps");
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Incidentally, the code you provided was of little use – it doesn't run by itself, and the user is required to guess values for $line_height and $out_line. I'd never used PostScript::Simple before, and this didn't make a lot of sense straight away. Anyway, the question was interesting.

Cheers