Create Alternate Access Mapping for Site Collection having deeper URL

Hi,

We have a sharepoint server named XYZ.domain.com , On that, there is a site collection with the url as /offices/site

So, now the portal is accessible as http://xyz/office/portal 

Now, we need to create friendly intranet URL for this portal as http://intranet.domain.com/

What I know is, we can create a CNAME record as intranetX.domain.com that points only to the server XYZ.domain.com on DNS and create AAM on the Sharepoint central admin.But, this will not help as the site collection is only accessible if we type in the deeper url.

Please advise how to acheive the below:

http://intranetX.domain.com/ -->http://xyz/office/portal 

Thank You,

Uman

Uman Ahmed