ASP.NET Caching Vary BY Param when we have ASP.NET Routing Values instead of Query String values

Question

Normally we can do caching and make dependency on Request.QueryString values like

  <%@ OutputCache Duration="15" VaryByParam="search" %>

The url for such may be like:

  http://localhost/default.aspx?search=name

But in my application i am using ASP.NET 4.0 routing where i am passing the id of a product like:

  http://localhost:1205/searchdetails/40563

or

    http://localhost:1205/searchdetails/40564

and so on.....

In this case i access the product id something as

 Page.Route.Value["product_id"]

In this case how should i make the dependency of page on this route value.

I am new to caching so i dont have any much knowledge of the same.

Do we need to do some custom caching.

Any help is appreciated.