@Todd_Rogers
Thinking about this a bit more, there are some parts of express tools that are added to the startup loaded applications, so these are likely registered for AutoCAD to load them up. It's more than just a copy and setting the Options support path.

I looked in the registry for registered applications on AutoCAD and express tools is not there. So next I went into the Support directory to look at the acad2020.lsp and could not find anything there.
Next I ran the 'ol ACADINFO command from the command line and that put out a text file telling me more about the installation. I found the following in that report.

This led me to check the acad2020doc.lsp file which is different for each language so it's under
C:\Program Files\Autodesk\AutoCAD 2020\Support\en-us
There was nothing in that file for express tools that I could find.
However, while looking in that directory, I did find the 'acetmain.mnl' file is in there. This adds the pop menu (old style menus) to the software.
So, back to your question, adding express tools to a computer via the windows command prompt... I still think that copy the directory (but now include the ..."Support/en-Us" or another language), and then adding the support paths, it should load up. I do not know of a way to add the support paths using windows command prompt though - I would guess you'd have to edit the registry profile to add that to it, and still usually will require closing/reopening a couple times to get AutoCAD to read it... I think.