I found something that might help you:
http://www.xfree86.org/current/XKB-Config.pdf

2.2 Advanced Configuration
Since XFree86 4.3.x you can use multi-layouts xkb configuration. What does it
mean? Basically it
allows to load up to four different keyboard layouts at a time. Each such layout
would reside in
its own group. The groups (unlike complete keyboard remapping) can be switched
very fast from
one to another by a combination of keys.
Let’s say you want to configure your new Logitech cordless desktop keyboard, you
intend to use
three different layouts at the same time - us, czech and german (in this order),
and that you are
used to Alt-Shift combination for switching among them.
Then the configuration snippet could look like this:
     Section "InputDevice"
         Identifier "Keyboard1"
         Driver "Keyboard"
         Option "XkbModel" "logicordless"
         Option "XkbLayout" "us,cz,de"
         Option "XKbOptions" "grp:alt_shift_toggle"
     EndSection
Of course, this can be also done at runtime using utility setxkbmap. Shell
command loading the
same keyboard mapping would look like:
     setxkbmap -rules xfree86 -model logicordless -layout "us,cz,de" \
               -option "grp:alt_shift_toggle"

there's no way to fix this in the kbd(4) driver.  it has no idea which keyboard
it's talking to, because the OS presents it as a single device.

on linux, if you want multiple keyboards with different layouts, you'll have to
use evdev (which should be gaining xkb support shortly).