You said you're running the command directly. So when you ask "Any idea what the [...] should be replaced with? This is what I've been struggling to find out" you should already have the classpath and other bits? If not, please explain how you launch minecraft and then we can assist. I seriously doubt you can set the jvm permgen settings at runtime.
If you're using script to launch as is common (such via upstart) you'll often find a JAVA_OPTS enviornment variable that you can set.