[Orgmode] Changing the heading separator from ** to ---** (twiki topic edition)

[Al]

Hello,

I generally use org-mode to edit twiki topics as it's full of marvelous 
features.

One of the main feature of org-mode I can't use is the outline capability as the
heading syntax is choosen by twiki not me, which forbids to use '****' for 
level 4 (this will be '---++++'). 

There was a thread on March 16th which was discussion something like this.

Something like this:
(add-hook 'outline-minor-mode-hook
      (lambda ()
        (setq outline-regexp "---\\++")
        (define-key outline-minor-mode-map [(tab)] 'org-cycle)
        (define-key outline-minor-mode-map [(control tab)] 'org-cycle)
       (define-key outline-minor-mode-map [(shift tab)] 'org-global-cycle)))

works perfectly in any-mode + outline-minor-mode.

However, I'd really like to use org-mode for all editing (tables, colors, links,
....)

Is there a solution to use org-mode and just change the heading separator from
* to ---+
** to ---++
*** to ---+++

etc

Thanks in advance.