The feature is indeed end of life, but the programming for it has not been stripped from the product thus far to allow legacy users a chance to upgrade without losing a feature that is in their production environment. There are no PGP Portable options in the SED GUI, but you can still create one using the Windows Explorer context menu when you plug in a USB drive.
That being said, PGP Portable can be very problematic. I have personally attempted to encrypt the same drive 7 times and failed, only to have it work on the 8th try, with no logical reason for it to have failed in the first place. I would recommend using the normal drive encryption for encypting external drives, though you will need SED installed on any computer you want to access the data from.
To answer the original question, you cannot install only PGP Portable. It is a part of the SED client package.
http://www.symantec.com/business/support/index?page=content&id=DOC7062 has the quick-start guide for PGP Portable with SED 10.3.2.