gistfile1.cs

    public interface ISuperSimpleViewEngineExtension
    {
        string Invoke(string content, dynamic model, IViewEngineHost host);
    }

    public class GistSuperSimpleViewEngineExtension : ISuperSimpleViewEngineExtension
    {
        private readonly Regex regex = new Regex(@"(?:@gist\[(?<id>[a-z01-9]*)\])", RegexOptions.Compiled | RegexOptions.IgnoreCase);
        private const string GistTemplate = "<script src='https://gist.github.com/{0}.js'></script>";

        public string Invoke(string content, dynamic model, IViewEngineHost host)
        {
            return regex.Replace(content, match => (match.Groups["id"].Success) ? string.Format(GistTemplate, match.Groups["id"].Value) : string.Empty);
        }
    }