[Grml] How to setup Xorg keyboard layout ?

Hello,

I'm trying to use the GRML iso image (with grml-rescueboot package) on computers with a special keyboard layout, a french-targeted dvorak-like layout called « bépo ».

I found how to setup the console layout, giving « keyboard=dvorak-fr-bepo » in CUSTOM_BOOTOPTIONS variable of /etc/default/grml-rescueboot, but didn't found how to setup the Xorg layout : it's a flavor/variant of « fr » Xorg layout (though it very different from classical french Azerty) ; I can setup in a shell with :

setxkbmap fr bepo

and following grml's FAQ, I tried « xkeyboard=bepo », « xkeyboard=fr(bepo) » without luck.

Could you tell me what syntax can we use in xkeyboard definition, or how to setup my Bépo keyboard layout (if possible) ?

Thanks, Fred.