Use the Volume+ hardware key on your N9 (and N950!) as shutter button in the Camera application. That's all! 😉
It's called hack because it's quick'n'dirty. The non-hack version of this would use the XTest extension + Xlib directly (from C/C++) instead of relying on the xresponse and xprop command line tools 🙂 But then again, this does the job for me.