asp.net-mvc - How to build custom URL link MVC

Question

There are some methods like the followings in UrlHelper class in MVC4

    public string Action(string actionName, object routeValues);

    public string Action(string actionName, RouteValueDictionary routeValues);

...but i want to change route values in every Action method calls for this I wrote CustomUrlHelper class like the following:

public class CustomUrl : UrlHelper
{  
    public CustomUrl()
        : base(HttpContext.Current.Request.RequestContext,RouteTable.Routes){}


    public string CustomAction(string actionName, string controllerName, string areaName, object routeValues, bool generateToken)
    { 
        RouteValueDictionary rvd = new RouteValueDictionary(routeValues);
        //some changes on route value dictionary


        return Action(actionName,controllerName, rvd);
    }


}

If we know action name controller name than every thing is OK, but if we just know a base URL and route value dictionary than my CustomAction method does not work.

Let's say if I have just a linkbase like A/B/C/D and RouteValueDictionary.

Now I want a method it gets baseUrl and RouteValueDictionary and produces complete link.