I've seen this idiom before and really dislike it for exactly the reasons you describe. My only suggestion, if you want to have a sort of "indented delimiter" is to convert your delimiter spaces to underscores. Using your example, you'd have:

    ($content = <<"____END") =~ s/^\s{1,4}//gm;
    <p>$name</p>
    <ul>
        <li>foo</li>
        <li>bar</li>
    </ul>
____END
    return $content;
[download]

This is resistant to the tab/space problem. On the other hand, it's not quite as clean, and you still have to adjust the regex when the indention changes.