x11vnc as a output monitor

I am trying to get my tablet as a display to xrandr.
I am using optimus (Dell L502X).

If I use the intel driver, there is a VIRTUAL1 display that I can use to map into the area I am exporting with x11vnc.
e.g. x11vnx -clip 5000x2000+2560+0

With the nvidia driver, I dont have something equivalent to VIRTUAL1.

A - Is there something? equivalent to VIRTUAL1 with Nvidia driver?

Some pages suggest to use an unused output like VGA-1 or HDMI-1. However it complains about no crtc.

Another option would be to not to use the virtual output at all.
Just map x11vnc to an offscreen area of the famebuffer.

This works fine, but the pointer cannot get to this area (thats whay the VIRTUAL1 output is needed).
An option in xorg.conf that would deal with this is ConstrainCursor which I already have it to off.

Right now, with a 3-head setup (1 nvidia and 2 intels), with ConstrainCursor on, the pointer would be locked on the nvidia display only.

So, my other question is:

B - How do I enable the pointer to go to an off screen area?

My setup is a non-retangular one. (1 - 2.5/4k above, 1 - 1.9k below and another 1.9k on the right).

Also, any other suggestions are very welcome.