[xmonad] action of "doFullFloat" upon pressing a key

[Christoph Groth]

Dear xmonad users,

I wasted several hours trying to find this out myself -- any help is
highly appreciated.

My xmonad.hs has

myManageHook = composeOne
	[ transience
	, isFullscreen -?> doFullFloat
	]

This makes

$ xpdf -fullscreen something.pdf

display on the whole physical screen.  However, it doesn't seem to work
with video players like vlc and xine.  I would like to have the effect
of doFullFloat upon pressing a key.  How would one tell xmonad to do
that?

thank you,
Christoph