> With current trunk you can try (experimentally)
>
> (display-buffer
>  (get-buffer-create "foo")
>  '((use-side-window bottom 0) (pop-up-window-set-height . 1)))

I tried this code and get funny results: typing `C-x C-b' displays
the *Buffer List* buffer in that small 1-line window :)

So this window should be marked as dedicated.  A more compact specification
to do that could look like:

  (display-buffer "*global-mode-line*"
                  '(minibuffer . above) (dedicated . t) (height . 1))