Ubuntu 16.04 CUDA support for Geforce 850m

I have tried all of the Ubuntu drivers from 340 - the latest 384 for Ubuntu 16.04.
340 is the only driver that works. But I am trying to get CUDA working on my Geforce 850m and the 340 driver doesn’t support CUDA. I have heard it might be a problem with Optimus.
I just want to check it see if anyone has CUDA working on a Geforce 850m under Linux.
Any help would be great.