(Information Below for 9.1.3 Environments)
To modify the Web Report component used from SAS Portal, modify the PortalContent.xml located in the Installation Folder (such as c:\Program Files\SAS\Web\Portal2.0.1\Portal\WEB-INF\content in windows) and then redeploy the Portal. (You can directly modify the same file in the Tomcat/webapps location, however modifying the installation folder ensures future redeploys will include this modification rather than having to re-do later when changing something else (like application timeouts)).

The only change required is below. We modified 'SASWebReportViewer' with 'SASWebReportStudio'. Note that the java code is sensitive to capital letters, must be exactly what the Java Webapp is called.

      <content ; interface="com.sas.report.repository.ReportEntryInterface"
                         category="report"
                         icon="Report.image"
                         isViewerExternal="true" 
                         viewer="/SASWebReportStudio/logonFromPortal.do"
                         appendSessionInfo="true"
                         newViewerWindow="true"
                         passObjectInSession="false"  searchFilter="com.sas.portal.filters.PortalReportFilter,com.sas.portal.filters.PortalReportAttributeFilter"  searchRepositories="OMR"
                     searchFoundationOnly="false"
                     version="2.0">
      </content>

(Thanks to Zencos co-worker David Barron for providing this quick tip!)