Nick Koretsky composed on 2017-05-11 10:20 (UTC+0300):

> This is not a mistake, this is a deliberate effort to avoid problems of
> multiple display in a single screen setup.

Other than using DVI and HDMI rather than dual DVI, and FOSS only,

<http://fm.no-ip.com/SS/Xorg/2head-3840x1200x108-nvGT218-big31-deb8TDE-priRight1200.jpg>

seems to describe what you are actually after, but I'm not sure I understand
what you are after, other than avoiding the screen locking problem that I'm not
finding here. I know I'm using one Xorg "screen", and don't think I understand
what problem multiple Xorg "screens" would solve for you.
-- 
"The wise are known for their understanding, and pleasant
words are persuasive." Proverbs 16:21 (New Living Translation)

 Team OS/2 ** Reg. Linux User #211409 ** a11y rocks!

Felix Miata  ***  http://fm.no-ip.com/