Forcing VGA output over Mini DisplayPort in Linux

For a long time adding multiple monitors to my laptop has JustWorked™ and have been a bit complacent about assuming that plugging into a random projector would be fine, but recently a VGA projector attached to the mini-display port was not detected (I think because it was attached to a VGA switch)

The below did allow me to force VGA output (even though xrandr never saw the VGA device)

xrandr --output eDP1 --mode 1024x768
xrandr --addmode DP1 1024x768
xrandr --output DP1 --mode 1024x768 --same-as eDP1

The graphics card is an Intel and I have the latest i915 drivers from 01.org

The xrandr output was

Screen 0: minimum 8 x 8, current 1920 x 1080, maximum 32767 x 32767
eDP1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 294mm x 165mm
   1920x1080     59.93*+  59.93
   1680x1050     59.95    59.88
   1600x1024     60.17
   1400x1050     59.98
   1600x900      60.00
   1280x1024     60.02
   1440x900      59.89
   1280x960      60.00
   1368x768      60.00
   1360x768      59.80    59.96
   1152x864      60.00
   1280x720      60.00
   1024x768      60.00
   1024x576      60.00
   960x540       60.00
   800x600       60.32    56.25
   864x486       60.00
   640x480       59.94
   720x405       60.00
   640x360       60.00
DP1 disconnected (normal left inverted right x axis y axis)
HDMI1 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)