I can't say I've ever tried this before. Something feels like it won't work unless you strip the jar apart and write to the correct place (doesn't sound like fun). What's wrong with writing and override configuration file that's just stored on a local machine? To me, the jar text file (sorry, I assumed its a config file which may be a poor assumption) should be kept intact in order to preserve a 'default' value.
I'll poke around the net as well to see if I can't find something regarding this.
header('HTTP/1.1 420 Enhance Your Calm');