Is it possible to add delay to concurrent requests in ASP.NET Web API 2?

I am using WebApiThrottle for rate limiting in my ASP.NET Web API 2 project, but I am having problems with concurrent requests. Instead of sending 429 too many requests responses, is it possible to delay concurrent requests, for example, allowing only one request per second? Here is my WebApiConfig:

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        // Web API configuration and services

        config.Formatters.JsonFormatter.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore;
        config.Formatters.JsonFormatter.SerializerSettings.DateTimeZoneHandling =
            DateTimeZoneHandling.Local;
        // Web API routes
        config.MapHttpAttributeRoutes();

        config.Routes.MapHttpRoute(
            "DefaultApi",
            "api/{controller}/{id}",
            new { id = RouteParameter.Optional }
        );
        config.MessageHandlers.Add(new ThrottlingHandler()
        {
            Policy = new ThrottlePolicy(perSecond: 1, perMinute: 20)
            {
                IpThrottling = true,
                EndpointThrottling = true
            },
            Repository = new CacheRepository(),
            QuotaExceededMessage = "You may only perform this action every {0} seconds."
        });

        config.MessageHandlers.Add(new RequestResponseHandler());
        config.Filters.Add(new CustomExceptionFilter());

        var resolver = config.DependencyResolver; 
        var basicAuth = (BasicAuthenticationAttribute)resolver.GetService(typeof(BasicAuthenticationAttribute));
    }
}