Функциональные клавиши (Fn) в awesome

а в чем проблема?
http://awesome.naquadah.org/wiki/FAQ

How to use a keycode in a keybinding?
You can use the format #XYZ for keycodes in your bindings. The following example shows a mapped multimedia/extra key, that's why the modifier is not present (but it could be):

awful.key({}, «#160», function () exec(«kscreenlocker --forcelock») end),

а дальше гугл по keycode и man xev