My appologies for bringing this up from the dead, but as it still comes up near the top of some google serches, it is still relevant.
xf86-video-intel v2.99, 22/Dec/2014, has a new tool.
Check and see if you have the tool 'intel-virtual-output' installed. This is included in 'xf86-video-intel' =< v2.99, aprox date released is 22/Dec/2014 Running 'intel-virtual-output' without any extra parameters will daemonize itself and detect attached displays in the background.
It will then perform all the trickery of virtualizing and cloning so that the newly attached screen can be used via conventinal screen management methods, such as cloning/extending with xrandr. The tool itself can be run with a standard bumblebee installation, as it will switch on bumblebee for access to the nvidia chipset.
If no displays are attached, or you are using the laptop display only, the tool can be killed so that bumblebeed can then disable the nvidia chipset for powersaving. To make it easier to kill 'intel-virtual-output' after running, start it in a console with the -f switch.
Usage: intel-virtual-output [OPTION]... [TARGET_DISPLAY]...
-d <source display> source display
-f keep in foreground (do not detach from console and daemonize)
-b start bumblebee
-a connect to all local displays (e.g. :1, :2, etc)
-S disable use of a singleton and launch a fresh intel-virtual-output process
-v all verbose output, implies -f
-V <category> specific verbose output, implies -f
-h this help
If no target displays are parsed on the commandline,
intel-virtual-output will attempt to connect to any local display
and then start bumblebee.
Games can be run on the external display via "export DISPLAY=:8", however they will not grab the mouse or keyboard properly. You will also need to start games with "primusrun" or "optirun" as per usual.