Is 3 monitors -> 2 X screens possible?

I have a workstation with a GTX760 and three monitors: two 27" and one 19". I want to have two X screens: one spanning the two 27s and the 19 as a separate X screen. Is this possible? I’ve read through the documentation, and I can’t figure out how to accomplish this.



Answering my own question…

Option “UseDisplayDevice” was the key.