Using OpenSCAD I imported and modified the original Hopper Upgrade STL to make it into an extension that can be stacked to enlarge the hopper to any reasonable capacity.

Note, I included the original poster's (drandolph) to see if it would render using the customizer since my OpenSCAD is having a problem outputting an STL based on that STL. I think it might be the same issue as is posted here: https://github.com/openscad/openscad/issues/191 .

I have not printed this yet, but as soon as I can get it to produce a valid STL I will.