I have googled this for the last half an hour, and found hits for pentaho parameters etc but nothing that appears to ask or answer this question.
I have a set of reports
OK, I have found a better solution using the little documented multi-tennant feature.
1) Stop Pentaho
2) Modify ( pentaho-solutions/system/pentahoObjects.spring.xml )
3) Add Suffix to Data Sources ( biserver-ce/tomcat/webapps/pentaho/META-INF/context.xml )
4) Delete /tomcat/conf/Catalina/localhost/pentaho.xml
5) Restart Pentaho, create a user someone@xxx etc etc
6) Create a report using the JNDI Name "MYDBSRC"
7) Login as someone@xxx and you will get a different report / datasource than either logging in as user, or user@aaa
Tadah !!