I've come up with an entirely better solution which leaves this script as it was prior to the use of the shell_exec, so there's no need to go the bash route anymore.

Now I'm just trying to figure out why my Automator solution works brilliantly as an app with drag and drop and directly from within Automator, but not as a print plugin. Having tried a really simple file-moving test, the best I can come up with so far is that Automator-based print plugins are not working in Mac OS X 10.8 at all at this time.