Script to enable/disable JRE 6 update 18

I'm new to the forum and scripting all together.  At work I have two web based applications that require different versions of JRE.  One requires JRE 6 update 18, the other JRE 5 update 9.  As I'm sure most of you know if there's multiple versions of JRE installed on a system, it'll default to the latest version.  This is a problem as I have an application that will only work in 5 update 9 and one that'll only work in 6 update 18.  I can go into the JRE control panel and disable 6 update 18, but it doesn't reenable itself when the application that calls for it is opened.  I need a script that'll enable JRE 6 update 18 in the JRE control panel when the application is launched and disable it when the application is closed.  Anybody have any advice as to how to do this?  Anybody else ever had to do something similar?
 
Thanks