Is it possible to use the integrated gpu on MBP retina with Bootcamp? I came across this page which demonstrates that simply two lines need to be changed in order for Windows to detect the integrated gpu and use it: http://community.secondlife.com/t5/Second-Life-Viewer/Enabling-Intel-Iris-Graphics-For-Bootcamp-Users/td-p/2535800

Does the above work and if so is it possible to manually control whether the integrated or discrete gpu is in use? Also, would it automatically switch over from discrete to integrated and vis-a-versa when the load requirements change?
No, sorry. Apple disabled switching between the (integrated) IGPU and GPU.

I haven't tested what you posted, and I doubt it will work. (Still 1.3 years left on my warranty)