RU4 came out with a new java-free version of LiveUpdate, which is apparently not silent anymore as per http://www.symantec.com/docs/TECH212353 (cannot confirm it, didn't test RU4 on MAC yet):
...queries the user on whether or not to update some things...
You can follow this procedure to run LiveUpdate via command-line, which is apparently always launched silently that way:
http://www.symantec.com/docs/TECH212349
If it works, you may use scheduler to run it at your convienience.