How To Use System.Web.Routing To Not URL Rewrite In Web Forms

I am using System.Web.Routing with ASP.NET (3.5) Web Forms that will URL rewrite the following URL from

http://www.myurl.com/campaign/abc

http://www.myurl.com/default.aspx?campaign=abc

The code is as below:

public static void RegisterRoutes(RouteCollection routes)
{
routes.Add("CampaignRoute", new Route
(
"{campaign_code}",
new CustomRouteHandler("~/default.aspx")
));
}
IRouteHandler implementation:
public class CustomRouteHandler : IRouteHandler
{
public CustomRouteHandler(string virtualPath)
{
VirtualPath = virtualPath;
}
public string VirtualPath { get; private set; }
public IHttpHandler GetHttpHandler(RequestContext
requestContext)
{
if (requestContext.RouteData.Values.ContainsKey("campaign_code"))
{
var code = requestContext.RouteData.Values["campaign_code"].ToString();
HttpContext.Current.RewritePath(
string.Concat(
VirtualPath,
"?campaign=" + code));
}
var page = BuildManager.CreateInstanceFromVirtualPath
(VirtualPath, typeof(Page)) as IHttpHandler;
return page;
}

However I noticed there are too many things to change on my existing aspx pages (i.e. links to javascript, links to css files).

So I am thinking if there's a way to keep above code but in the end rather than a rewrite just do a Request.Redirect or Server.Transfer to minimize the changes needed. So the purpose of using System.Web.Routing becomes solely for URL friendly on the first entry.How to ignore the rest of the patterns other than specificed in the code?