Loading Java plugin from a specified location on client's disk?

I have done this before, but don't recall just how. I want to be able to load the Java browser plugin from a non-standard location on the browser client's disk. So, an internal corporate user visits my webapp, and I detect that they run Windows Vista, and that the java code should run under the plugin/jre in the path c:\corpsoft\sun\java6mod{.etc.}.

I understand that the client usually has their plugin load from the default location, but how can a web server tell the client where to load it from?

I know I have done this once in the past, so thanks for any suggestions!!!

This may be a security threat in some environments and that is why I am interested...