Best solution to force MacBook Pro 2011 to use integrated graphics (discrete graphics still working though)
The only walk-around, that works is described here: How to disable discrete graphics card and use only integrated graphics MacBook Pro Early 2011?. In short: remove kernel drivers for the discrete gfx card. It will make the MacOs work in the fallback mode without 3d acceleration. 

To control the brightness of your screen, I recommend to use: brightness slider. Because, the standard way of changing screen brightness will not work.

ps. The only way, I know, is to overheat your Mac as suggested here and use gfxstatus to force MacOS to use the integreted gfx. Still, MacOS might switch back to discrete gfx for some applications.

If you want to change OS, check this question: Can I use Linux in a 2011 Macbook Pro with a defective discrete GPU?