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>
More details on this can be found in the Mapping Publication IDs to friendly URLs page 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.