Looks like you found the URL just as I was typing my post.
(Caveat: everything I'm about to say applies to my Linux system; the filenames/directories may be different in the Mac package you used, so you may have to hunt a bit.)
CUPS-PDF by default sends the output files to /var/spool/cups-pdf/${USER}, where "${USER}" is the username.
IIRC, I had to actually edit the /etc/cups/cups-pdf.conf file manually to change it. Open the file in a text editor and look for something that looks like this line:
> #Out /var/spool/cups-pdf/${USER}
Remove the # and change the path to wherever you want the output to go, then save the file.
