How to run Weston on specific devices?

[me at beroal.in.ua]

Hello. My computer has 2 seats. By seat I mean a set containing a 
monitor, a videocard, a mouse, and a keyboard. I can drive them with 2 
Xorg server, and I am looking for how to replicate this configuration 
with Wayland.

AFAIK, Weston uses "libinput", so I assigned "WL_SEAT" of input devices 
to "seat1" using "udev" rules according to
http://wayland.freedesktop.org/libinput/doc/latest/udev_config.html . I 
run "weston-launch" with a configuration file {{{
[output]
name=card1-VGA-2
seat=seat1
}}}
Weston drives the wrong videocard and the wrong input devices. I see in 
its "stderr" that it is scanning all devices.