Is it possible to start recording with a GoPro without the official app or from an unsupported device?
For the GoPros with wifi (Hero3, Hero3+ or HD Hero/HD Hero 2 with a wifi bacpac), yes it is possible. They essentially work as a web server, so you can connect to that, and control the camera. It seems this is not officially documented anywhere, but a number of people have figured out how it works.
So turn on the wifi on the camera, then you can connect to it from your computer.
You can view the webserver by going to
http://10.5.5.9:8080 in a browser. This will let you view photos or videos stored on the camera.
To control the camera, you can send HTTP requests. eg to turn the camera on:
http://10.5.5.9/bacpac/PW?t=password&p=%01 (where password is the GoPro wifi password). And to trigger the shutter:
All of the commands are listed in this Github: KonradIT/goprowifihack