episerver url rewriting, put this in a template page's code-behind .cs

gistfile1.cs

protected string ResourcePath
{
    get
    {
        return
            _pageFilesUrl ?? (_pageFilesUrl = ResolveUrl(String.Format("~/PageFiles/{0}/", FolderId)));
    }
}

private int FolderId
{
    get
    {
        return (int)GetPage(CurrentPage.ParentLink)["PageFolderID"]; // todo: cope with html files in subdirectories when looking up folder
    }
}

private string ReplaceUris(string html)
{
    // get any old property to gain access to instance method ReplaceHtmlLinks()
    var propertyData = CurrentPage.Property[0];
    // translate relative links to absolute links that match the static file storage in PageFiles
    return html == null ? String.Empty : propertyData.ReplaceHtmlLinks(html, TranslateUri);
}

private string TranslateUri(string url)
{
    // alter any relative urls found
    return Uri.IsWellFormedUriString(url, UriKind.Relative) && !url.StartsWith("/")
                ? ResourcePath + url
                : url;
}