Simply disable short open tags with the short_open_tag
directive. The precise mechanism depends on how you run PHP.
Right, I've just seen your edit about not wanting to use this. Then, this question is becoming subjective since it depends on your idea of what more elegant means.
If using a variable/constant is more elegant:
<?php
define('XML_INIT', '<?xml');
?>
<script id="svg-xml" type="text/template">
<?=XML_INIT?> version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<etc />
</script>
If using an external file is more elegant:
<script id="svg-xml" type="text/template">
<?php readfile('./template.svg'); ?>
</script>
If using heredoc is more elegant:
<script id="svg-xml" type="text/template">
<?php echo <<<EOM
<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<etc />
EOM
?>
</script>