In the past, I've read a bunch of posts stating that it can't be done.
But I just read a blog entry that kinda turns that on its ear.
www.jarodschultz.com/revit-wallface-based-family-trick/
Don Ireland
Engineering Design Technician
There are specific Family Categories that can be the subject of Copy/Monitor - make sure that the original Family is of one of the valid Categories (you can change it back afterwards). You can sift through Revit Help to see if you can find the specific list, or you can just use Plumbing Fixtures.
I think it may be an MEP thing. This video http://www.youtube.com/watch?v=SpDDl4zdxSA shows a Coordination Settings button in the Copy Monitor Tools panel that I don't have and can't find. The elements I can monitor are Levels, Grids, Columns, Walls and Floors. I tried using Revit instead of Revit Architecture with no luck.