cups-pdf custom args

[Jack]

using cups 1.4.2 with the cups-pdf driver that comes with it, I see 6 arguments.  This is nice - one in particular I've been looking for - originating-host-name is really nice!  THanks!

So, I'm looking to hack on this a bit.  I want to include a place for an extra string - be it email, identifier, etc.  You see, I run a ton of automated jobs, and having the machine identifier with the doc name is 99% all I need, but there are cases where I need more.

An identifier string that I could place would be handy. Something like
http://printserver:631/printers/zPDF?identifier=pathology_reports

I think this is pretty doable, but I just want a pointer as to where I'd be looking for this.