Help mode keybindings

[Emanuel Berg <embe8573@student.uu.se>]

How do I bind C-j to "jump-to-register" in help mode?

I'd like that globally, so I bound it so in .emacs. But, in some modes
it was bound locally. For example, in "Lisp Interaction" mode, I had to
locally unset C-j to clear the path to the global binding, and this
worked with no problems:

(add-hook 'lisp-interaction-mode-hook
          (lambda () (local-unset-key (kbd "C-j"))) )

But, that didn't work for Help mode: the local binding wasn't
dropped. Not even setting it explicitly work, as in the below
code. Strangely, the "j" (not C-j) version worked!

(add-hook 'help-mode-hook
 (lambda ()
  ; ...
  (define-key help-mode-map (kbd "j")   'jump-to-register)    ; works
  (define-key help-mode-map (kbd "C-j") 'jump-to-register) )) ; not so

Are the Help mode keybindings set in stone?
-- 
Emanuel Berg - programmer (hire me! CV below)
computer projects: http://user.it.uu.se/~embe8573
internet activity: http://home.student.uu.se/embe8573