Now I can use xrandr to turn on and off rudimentary screen mirror.
xrandr --output VGA --auto
xrandr --output VGA --off
I'll update here when I successfully get the desktop spread across both screens. As a word of warning, I just turned of xrandr VGA output (--off) and all running applications were locked. I could swap focus between them but the applications themselves did not respond. Beware.