Not sure about the Mac setup...sorry.
Are you just installing the Mogrify plugin are are you installing the Piglet functionality. It's the Piglet stuff that most likely adds the extra GUI. I installed them all at the same time, so I'm not 100% sure. Apologize for not being more specific ealier...hope I didn't waste our time there.
Here is the link to Jeff's Piglet manager:
Piglet Manager
Once you install the piglet manager and configure it (basically point it to the ImageMagik Mogrify App), you can then drop in Timothy's piglet version of Lr/Mogrify. There's also piglets for SmugMug, flikr, Zenfolio, etc. I know the SmugMug one works flawlessly.