Importing from Rhino into PFC

I have created a very simple cone shape in Rhino and saved it as an .stl file. Once I’ve imported into PFC3D, I would like to be able to fill it with balls so that I can model those balls as particles (i.e. I am modelling a volcanic dome and would like to therefore not just have a geometry, but particles that are heaped in that shape). Does anybody know how to create particles from a geometry?

Many thanks!

Hi Claire- there is no provision for this in plain Rhino, but Grasshopper in combination with a plug-in like Kangaroo might be useful -