My first thoughts were, I wonder if anyone has come up with a way to have a video appear as a webcam (e.g. I'm skyping with someone, but the video and audio they see is some video I chose instead). After searching around a bit, it looks like people have done this video piping (as discussed on Manipulating Dev Video and Fake a webcam using a video loopback device?
As mentioned in your comment,
gst-launch v4l2src device=/dev/video0 ! v4l2sink device=/dev/video1 allows you to duplicate video0 to video1, and video1 is readable by some software.
In order to have this run when your computer starts, you can follow the UbuntuBootupHowto to come up with something like:
start on runlevel 
stop on runlevel 
exec gst-launch v4l2src device=/dev/video0 ! v4l2sink device=/dev/video1
This script should start when the computer boots and also allows you to run
sudo service videocloner start|stop (Note: if my example script doesn't work, try moving
gst-launch v4l2src device=/dev/video0 ! v4l2sink device=/dev/video1 into a shell script, and changing the
exec line to call your shell script instead).