plugins - how to set default java plug-in version

I can set the jre version from the Control Panel -> Java -> Java Runtime Environment Settings. But I cannot figure out how to change the Java Plug-in Version. I would like to use an earlier java plug-in version, like 1.5.0_12. How can I do that? Thanks

Here is the output in the Java Console:

Java Plug-in 1.6.0_19 Using JRE version 1.5.0_12-b04 Java HotSpot(TM) Client VM