Chromium kiosk mode with 2 monitors - help needed

[Peter]

Chromium version: 36.0.1985.125
OS: Ubuntu 14.04 64-bit

Hello.

I'm trying to run Chromium in kiosk mode in dual monitor environment
(two identical monitors, 1280x1024 resolution each, the second one placed below the first one).
Basically, I want browser window to be stretched so that the upper half of a website
is displayed on the monitor at the top and the lower half on the monitor at the bottom
(I hope it's obvious what I want to achieve).

Without the kiosk mode, I can use the following command to invoke the browser:

chromium-browser --window-position=0,0 --window-size=1280,2048 <URL>

and it works perfectly (the height of my virtual screen is 2048 as it's the height of two monitors combined)

Unfortunately, when I add the --kiosk flag to the above command so it looks like that:

chromium-browser --window-position=0,0 --window-size=1280,2048 --kiosk <URL>

the display gets completely messed up: the monitor at the top doesn't display anything
(black screen, but the mouse cursor still shows there if I move it up), the whole content
is moved to the other monitor. I figured out why it happens: whenever I try to stretch
the display beyond the first monitor in kiosk mode, the display of the first monitor
gets pushed by as much as I want to add to the second monitor.
Here's an example: if in command above --window-size=1280,1124, then
the monitor at bottom would correctly display first 100 lines below last line
displayed on the monitor at top, BUT first 100 lines on the first monitor
would be black).

Basically, how can I force Chromium to display a browser window on
two monitors in kiosk mode? Chromium must be invoked without user
interaction, so I'm asking for an appropriate command line to solve my
problem. Thank you in advance.