Assuming that the whole of the website Publication is published out to the virtualDirectory folder (i.e.  the '`Publication URL`' is virtualDirectory), then you can map this in the `cd_dynamic_conf.xml` file (within your website's `/bin/config` folder and the Content Delivery Webservice) using a Publication element:

    <Publication Id="95">
       <Host Domain="somedomain" Port="80" Protocol="http" Path="/virtualDirectory"/>
    </Publication>

![enter image description here][1]

More details on this can be found in the [Mapping Publication IDs to friendly URLs page][2] in the online documentation (login required).

** Caution: The following note is given in this page of the online documentation:

> Note that this functionality is only supported for the Java Content
> Delivery Web service, not the .NET Content Delivery Web service.


  [1]: https://i.sstatic.net/PfYDn.png
  [2]: http://sdllivecontent.sdl.com/LiveContent/content/en-US/SDL_Tridion_2013/task_7D1E9C4C050E422F92E357FC621DC99E