Help overriding gallery_shortcode default markup

By default, WordPress uses some very nasty code to output galleries using the gallery shortcode. This is managed from wp-includes/media.php, specifically by the next function:

function gallery_shortcode($attr) {
	global $post;

	// Allow plugins/themes to override the default gallery template.
	$output = apply_filters('post_gallery', '', $attr);
	if ( $output != '' )
		return $output;

	// We're trusting author input, so let's at least make sure it looks like a valid orderby statement
	if ( isset( $attr['orderby'] ) ) {
		$attr['orderby'] = sanitize_sql_orderby( $attr['orderby'] );
		if ( !$attr['orderby'] )
			unset( $attr['orderby'] );
	}

	extract(shortcode_atts(array(
		'order'      => 'ASC',
		'orderby'    => 'menu_order ID',
		'id'         => $post->ID,
		'itemtag'    => 'dl',
		'icontag'    => 'dt',
		'captiontag' => 'dd',
		'columns'    => 3,
		'size'       => 'thumbnail',
	), $attr));

	$id = intval($id);
	$attachments = get_children( array('post_parent' => $id, 'post_status' => 'inherit', 'post_type' => 'attachment', 'post_mime_type' => 'image', 'order' => $order, 'orderby' => $orderby) );

	if ( empty($attachments) )
		return '';

	if ( is_feed() ) {
		$output = "\n";
		foreach ( $attachments as $id => $attachment )
			$output .= wp_get_attachment_link($id, $size, true) . "\n";
		return $output;
	}

	$listtag = tag_escape($listtag);
	$itemtag = tag_escape($itemtag);
	$captiontag = tag_escape($captiontag);
	$columns = intval($columns);
	$itemwidth = $columns > 0 ? floor(100/$columns) : 100;

	$output = apply_filters('gallery_style', "
		<style type='text/css'>
			.gallery {
				margin: auto;
			}
			.gallery-item {
				float: left;
				margin-top: 10px;
				text-align: center;
				width: {$itemwidth}%;			}
			.gallery img {
				border: 2px solid #cfcfcf;
			}
			.gallery-caption {
				margin-left: 0;
			}
		</style>
		<!-- see gallery_shortcode() in wp-includes/media.php -->
		<div class='gallery'>");

	foreach ( $attachments as $id => $attachment ) {
		$link = wp_get_attachment_link($id, $size, true);
		$output .= "<{$itemtag} class='gallery-item'>";
		$output .= "
			<{$icontag} class='gallery-icon'>
				$link
			</{$icontag}>";
		if ( $captiontag && trim($attachment->post_excerpt) ) {
			$output .= "
				<{$captiontag} class='gallery-caption'>
				{$attachment->post_excerpt}
				</{$captiontag}>";
		}
		$output .= "</{$itemtag}>";
		if ( $columns > 0 && ++$i % $columns == 0 )
			$output .= '<br style="clear: both" />';
	}

	$output .= "
			<br style='clear: both;' />
		</div>\n";

	return $output;
}

What I want to do is override this function and use an ul with no style tag in the middle of my body. Searching around, I found some useful pieces of code and managed to write this:

function remove_gallery_css()
{
	return "<ul class=\"gallery\">";
}
add_filter('gallery_style', 'remove_gallery_css');

function fix_gallery_output( $output )
{
	$output = preg_replace("%</div>%", "</ul>", $output);

	return $output;
}
add_filter('the_content', 'fix_gallery_output',11, 1);

The first functions removes the <style> tag and works like a charm. It also removes the <div class=”gallery”> and replaces it with an ul. The problem comes with the second function. It basically removes any </div> from the_content and replaces it with an /ul
. Works perfectly unless you have a </div> (div end tag) somewhere else in your posts/pages.

Si the question is, how do I replace the gallery_shortcode output of </div> with an /ul without affecting anything else? Of course, I could hack media.php, but I’d like to distribute this as a plugin so people won’t have to hack media.php