Hi Matthew.
I have a converter which takes in mm5 model data and outputs CF-compliant netcdf. The netcdf files load fine into the IDV. The
following url should get you an example file (about 40meg)
http://metoc.apl.washington.edu/uwme/netcdf/2007120700-eta-d2.nc
Also, we provide a zip of the converter, including the Java sources:
http://metoc.apl.washington.edu/uwme/downloads/edu.washington.apl.mm5v3tonc.zip
I recall that in producing the CF compliant nc, the nc file does not actually need any lat or lon variables in it at all, just
the correctly named Cartesian x and y and the projection variable.
I hope this may help, feel free to ask questions
Stuart