Are you sure this is a "design kit" problem (like, I work
in silicon using Cadence where a PDK is a bundle of
all views and rules and models needed to do a chip
design in a specific process) or is just a rack of
model files as .inc or .lib SPICE files that would get
selectively invoked when / where you need them?
If you only need one device model from the pile, can
you just extract it to a fave models director and add the
.include (presuming ADS language is SPICE-like, I do
not and have never used) to the netlist or as a schematic
based directive, to "hook it up"?