If you want to make a template with graphics software and place it on your PostScript page, one way to do it is with an eps file.
<?php
$template = ps_open_image_file($ps, 'eps', 'template.eps');
ps_place_image($ps, $template, 0, 0, 1);
?>
Professional page layout software such as InDesign will typically be able to generate an eps file. If your software can't, one way to do it (on Windows) is to set up a printer that prints to file with the driver "Lexmark Color 4079 plus PS". This driver is included with Windows and has the option in its advanced preferences to generate an EPS file.