Is there a way to make a key really unbound?

[Eli Barzilay <eli@barzilay.org>]

I'm trying to properly address a request to make calculator.el treat
"E" as if it were "e" since there is no binding specifically for "E".
This works in the electric mode since it specifically uses the
`calculator-mode-map' as a global map, which means that the unbound
"E" gets translated to its bound unshifted version.  However, in the
regular non-electric mode this can obviously not be done.  (If it is,
then the shift translation works as intended, but the global map is
lost...)

I think that this is because "E" gets the default
`self-insert-command' binding from the global map, which is then
translated to `undefined' due to my use of `suppress-keymap'.  I tried
to manually tweak that remapping to `nil' which doesn't help.

So, is there some way to make a key really unbound -- rather than
getting `undefined'?  Or, is there some other way to bind a key to
some "try-this-key-with-shift-off" function?

(Without this, the only thing I can think of is to make the code that
sets up the map explicitly bind upper-case letters too when a
lower-case binding is made, but that sounds like an ugly hack.)

-- 
                    ((x=>x(x))(x=>x(x)))                   Eli Barzilay:
                    http://barzilay.org/                   Maze is Life!