Create a remote session able to use a screen larger than allowed by remote hardware

Question

I am trying to use an ubuntu 14.10 laptop with a large screen (2 monitors actually) which size is way larger than its graphics card limits. So I thought to use it via LAN (1Gb/s):

with "ssh -X ..." I can start applications on that laptop from a kubuntu 15.10 desktop PC (which has powerful graphics) connected to the large monitors and see those applications on them.

But now I would like to open remotely the entire gnome session.

I tried KRDC from the desktop but I can only join the current low resolution session running on the laptop, getting a window of its screen size.

Then, on the desktop, from the console CTRL-ALT-F2, I executed this:

sudo ssh -X username@192.168.1.2 gnome-session

but it did not do anything, just return to local prompt.

My questions are:

• Is the use of "ssh -X ... gnome-session" a reasonable way to do it and I should just try it harder?
• I would prefer to have that gnome-session on a resizeable window (like a virtual machine) to be able to use other applications on the desktop at the same time. Is there a way to do it?
• Is there a simpler way? (I have seen hw adapters to connect USB3 to 2 2560x1600 monitors, but are quite expensive and I have no clue if they work well with ubuntu and about their image quality).

Many thanks,

Yandot