Don't know if you want to use Razor. Here is a slightly changed version of Cultiv his Razor sitemap:

@ListChildNodes(Model.AncestorOrSelf(1))

@helper ListChildNodes(dynamic startNode)
{
    Response.ContentType = "text/xml";
    const int maxLevelForSiteMap = 100;


    foreach (var node in startNode.Children
        .Where("HasAccess")
        .Where("!IsProtected")
      )
    {
        if(node.template > 0 && !node.umbracoNaviHide) {
            <url>
                <loc>@GetUrlWithDomainPrefix(node.Url)</loc>
                <lastmod>@(string.Format("{0:s}+00:00", node.UpdateDate))</lastmod>
                @if (node.SearchEngineSitemapChangeFreq.ToString() != "")
                {
                    <changefreq>@node.SearchEngineSitemapChangeFreq</changefreq>
                }
                @if (node.SearchEngineSitemapPriority.ToString() != "")
                {
                    <priority>@node.SearchEngineSitemapPriority</priority>
                }
            </url>
        }

        if (node.Level <= maxLevelForSiteMap && node.ChildrenAsList.Count > 0)
        {
            @ListChildNodes(node)
        } 
    }
}

@functions {
    private static string GetUrlWithDomainPrefix(string url) {
        if (url.StartsWith("/"))
        {
            url = url.Substring(1);
        }

        var domainPrefix = string.Format("http://{0}/", HttpContext.Current.Request.ServerVariables["HTTP_HOST"]);
        if (url.StartsWith(domainPrefix))
            return url;
        else
            return domainPrefix + url;
    }
}

The difference is that it will look at the children even if a parent has umbracoNaviHide set to true. So this means you can set a umbracoNaviHide to true and still display it's children if those have umbracoNaviHide set to false. Hope this is what you're looking for.

Jeroen