I know that the Fruitz of Dojo port at http://www.fruitz-of-dojo.de/php/download.php4?dlnr=2
has a little command line utility that lets you type in command line parameters.
Maybe you could rename the Mac ProQuake executable to the name Fruitz of Dojo uses and use that utility to enter the command line parameters.
Like type in the command line "-game whatever -dedicated 16 +map start" or whatever you need the command line to be.
/I don't have a Mac, but I tried Quake on the Mac about 2 years ago