I edited this using Blender
For this I simply imported the model into Blender and added a circle mesh with n-gon faces. I extruded it up to add some volume, then merged the objects. Exported it as stl and voila.
RockgnomeRecluseWithBase.blend | 16.7MB | |
RockgnomeRecluseWithBase.stl | 11.2MB | |
RockgnomeRecluseWithBaseSplit.blend | 11.1MB |