In older versions of spectre that don't support localParam, or doing this sort of funny thing with the global params in the cdf, what I did was to add a subcircuit to my modelfiles that would turn the modelfile parameter of interest to a voltage or current of a DC block.
With a structural instantiation of that block, I had access to the variable for my testbench controller. back in 2007 on ic5141 that was about the only way to do it.
I think I may have documented this in one of my 2007 papers?
(see bmas 2007 archives) at
www.bmas-conf.org for one of them.
Of course a better way to do this is always preferred.
jbd