Mark, I think you can try doing that already with the use of iw_watermark_display filter hook.

Try copying that to functions.php of your theme.

function custom_iw_watermark_display($attachment_id) {
	// do this in admin only
	if (is_admin()) {
		// get uploaded file url
		$attachment_link = get_attachment_link($attachment_id);
		// check if file path points to woocommerce upload folder
		if (strpos($attachment_link, 'woocommerce_uploads') !== false) {
			// if it does, disable watermarking of this specific image
		    $attachment_id = false;
	return $attachment_id;
apply_filters('iw_watermark_display', 'custom_iw_watermark_display');