Since saszipam is undocumented and unsupported, that may be hard.
Using the documented approach with winzip, http://support.sas.com/kb/26/011.html
you could specify the wzunzip option to list the contents rather than to transmit the contents of one specific file.
Ready to join fellow brilliant minds for the SAS Hackathon?
Build your skills. Make connections. Enjoy creative freedom. Maybe change the world. Registration is now open through August 30th. Visit the SAS Hackathon homepage.