Sure! For -vgui, in the VM, navigate to this location:
/home/default/.config/autostart
and edit (right-click->open with->gedit) the Steam.desktop file. At the end of the "Exec" line, add "-vgui" and save. Since this is the autostart file, I would do a container restart. I believe you can edit the Steam executable itself, so it will start with -vgui enabled whenever you open Steam, but I did it the autostart way. When the container restarts, Steam should load up. At this point, only the store page was loading for me. In Steam, on the top menu, click "View -> Small Mode". Your steam library games list should pop up. You can also switch to Big Picture mode from the View menu, but like I said, I have not had success with that.
Edit: it is worth noting that as time goes on since the new Steam UI was launched, the old UI seems to get more and more broken, so there may be a point where this workaround will not work at all