I still find it strange that I'm only observing this behavior in 2018, and not also 2016 (I uninstalled 2017 when 2018 became available).
That said, I've experimented for the past few minutes, and think I've found an easy solution that is working in 2018 here, and presumably the same for other versions as well.
Simply create a Script (.SCR) that loads with /b switch in the application icon's Target path, such that the Script sets the desired workspace.
Example application icon Target path:
Code:
"C:\Program Files\Autodesk\AutoCAD 2018\acad.exe" /ld "C:\Program Files\Autodesk\AutoCAD 2018\\AecBase.dbx" /p "<<C3D_Imperial>>" /product "C3D" /language "en-US" /b "foo.scr"
Example "FOO.scr" (found in top SFSP):
Code:
(setvar 'wscurrent "Civil 3D")
** Note that there's a space after closing paren
Cheers