MacOS – this flickering menu bar icon

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.

Looking at the position, it seems to be an app from Apple.

Press Command and drag & drop it out of the menu bar.