No, I can't find any way to compile Processing files from the command line. Despite the fact that they claim they've added this feature in (reply #7), there's no mention of how this actually is done.
I looked over the instructions on converting Processing code into Java code and its essentially adding in the necessary libraries and wrapper classes. Of course, in practice it looks to be unfeasible (as your initial question showed) to do on your own.
I'd say your best bet is to pester the guy on the given link who said he added it in and ask for some documentation on how it's done. Furthermore, I think you can get the bug re-opened since it doesn't count as a bug fix if they don't tell you how to do it, or at least a reference to the manual showing where this is discussed.