How to devote one GPU to CUDA, the other to desktop graphics, in Ubuntu 16.04

I’m running Ubuntu 16.04 and have two cards installed:
$ lspci | grep -i vga
01:00.0 VGA compatible controller: NVIDIA Corporation GP102 [TITAN X] (rev a1)
08:00.0 VGA compatible controller: NVIDIA Corporation GM107 [GeForce GTX 750 Ti] (rev a2)

I’d like to specify the Titan for compute, and the 750 for running the desktop. I found this post but I think the Xorg configs have changed since then: https://stackoverflow.com/questions/21911560/how-can-i-set-one-nvidia-graphics-card-for-display-and-other-for-computingin-li

Anyone have updated instructions?

Thanks!