Any way to get a super modifier on Ubuntu?

[Sean McAfee]

I recently started using Emacs on Ubuntu, and am having trouble getting
my usual configuration working.

I have a number of commands bound to a key combination involving the
super modifier.  I'd like to associate this modifier with the
"windows" key on my Dell keyboard.  When I open the Ubuntu Keyboard
Preferences window, my choices under "Alt/Win key behavior are":

* Default
* Add the standard behavior to the Menu key
* Alt and Meta are on Alt keys
* Alt is mapped to Right Win, Super to Menu
* Control is mapped to Alt keys, Alt is mapped to Win keys (*)
* Control is mapped to Win keys (and the usual Ctrl keys) (*)
* Hyper is mapped to Win-keys
* Left Alt is swapped with Left Win (*)
* Meta is mapped to Left Win
* Meta is mapped to Win keys

Except for the items marked with a (*), Ubuntu continues to intercept at
least some key combinations involving the windows key.  For example,
windows-w causes all of the onscreen windows to be shrunken and tiled.
super-w is one of my Emacs chords, so only the starred items are
possibly appropriate.  Unfortunately, none of them gives me a super
key.

The "Hyper is mapped to Win-keys" is the best option I've found so
far, in that the windows key is associated with Emacs's hyper
modifier.  It's a pain to have to change all my chords from super to
hyper, but it might be tolerable if some chords were not still
being intercepted by Ubuntu.

Ideally, I'd like the left windows key to do nothing except be Emacs's
super modifier, at least when the Emacs window has focus.  The right
windows key could still retain its special Ubuntu functionality,
should I ever want to start using it.

Is there any way to get the behavior I want?  In the past I've
sometimes twiddled X using xmodmap et al. in situations like this, but
my impression is that techniques like that don't work well with modern
window managers, which like to assume all such responsibilities for
themselves.