Change the location of an icon in the menu bar?
If a menu icon is allowed to move, command + mouse select will work.

You might have to patch the program (or System Ui Server). Have you asked the developer if they can implement this as a feature?

Only the Apple icons are movable on my 10.6.7 systems so it certainly isn't easy for a developer to get this working and may be impossible in practice. 

The only workaround would be to have a script that delays the radium start as the leftmost item is the last to load. If you had a launch script that slept for 3 minutes and then killed, relaunched that app - it would be leftmost until another started... If it was really important, you could kill and relaunch it periodically every X minutes to ensure that over time it's the leftmost icon without you taking manual action.