Hi Teddy,
I think the simplest thing would be to change the resulting Complex Shape's Fill Type from "None" to "Opaque" using the TF Element Info tool.
Would that work for you?
The only other option I can think of (which I haven't tried) is to assign the Region to a specific Family + Part within PC Studio, and have that Part using a rendering material that includes a Geometry Map with a dense hatch to represent the fill.