Yes you can, but you need to make your own update packages, apply a certificate to them, and then import them into WSUS. It's known as Local Publishing.
The WSUS API allows you to create and publish custom updates, applications, and device drivers for your organization. The process of authoring and distributing this kind of update is called local publishing. Local publishing is best performed by organizations that have dedicated development and testing resources, since the planning, implementation, testing, and deployment of custom updates is a complex and time-consuming process.
Check out http://localupdatepubl.sourceforge.net/:
Local Update Publisher allows system administrators to publish their own updates to Windows Server Update Services using local publishing.
Check out http://wsuspackagepublisher.codeplex.com/:
Wsus Package Publisher allows you to publish your own updates as MSI, MSP or EXE files. Hence, you can deploy applications like Adobe Reader, Java, Flash Player or Symantec Endpoint Protection 12.1. and update them.
Couple alternatives to using WSUS: