Problem changing font properties

I am in the midst of battling the OS X postscript font idiosyncrasies.
I wish to switch to:
  font.sans-serif : Bitstream Vera Sans

so that I can produce usable postscript files. This works fine if I edit the matplotlibrc file and run the code.
BUT I figured it would be better to do this in the code, since I only want this for the PS backend.
I thought that the following should produce the same result as editing the matplotlibrc file but it apparently does not.

fontDict = {'family':'sans-serif',
             'style': 'normal',
             'weight': 'medium',
             'size': 12.0,
             'sans-serif':['Bitstream Vera Sans']}

What (probably obvious) am I missing?
By the way pylab.rc('text',usetex = True) works fine for me to yield good PS.