[ltp] T41: FN-key as a modifier?

[Felix E. Klee]

I'm in the process of switching from an iSeries 1200 to a T41.  The
iSeries a had the Windows keys and I enjoyed the left one as a modifier
for keyboard shortcuts of several window manager functions (FVWM).  Now,
as the T41 doesn't have any Windows keys, I'd like to use the FN key for
that purpose, but I haven't found a way to make it work as a modifier in
X.org 6.8.2.  Here's what I've added to my "~/.Xmodmap":

  keycode 227 = Super_L add Mod4 = Super_L

The key works, but - as "xev" shows - when it is pressed, other keys
that are pressed are ignored, i.e. it seems like the FN-key somehow
blocks the keyboard.  So:

How do I make the FN-key work as a modifier key?  Any ideas?
-- 
Felix E. Klee