There is an Xposed Module that enables the OK google command for just about any third party launcher. Sense launcher, Apex, Nova, and just about every other launcher you can think of. Simple, install Xposed framework, enable, reboot. Install Ok google module, enable, reboot, done. It's cool that Nova natively supports it now though. I'm sure Apex will follow suit. That was the only feature that had me using the otherwise crappy GEL launcher.