Cruises - Get Carnival OBC with frequent flyer miles or hotel points?

Is it possible to get Carnival OBC by using frequent flyer miles or hotel points? I realize Carnival has a Mastercard I could apply for, but the current offer didn't seem very generous, e.g. around $50 OBC only.

So I'm wondering if any other programs would let me buy Carnival on board credit.

I have miles / points with the following:

* BA
* UA
* CO
* US
* DL
* Hilton
* Marriott
* Starwood

Thinking of getting an AMEX MR card. Can MR points be redeemed for Carnival OBC? And I'd love to liquidate my Delta skymiles as well as my US Airways miles. Don't have a heck of a lot in those accounts. Would be fun to use for OBC.

If not Carnival, what about RCL?

Far as I know, with the little bit of research that I did for RCCL, nothing like that exists :(

You can get Carnival OBC by being a stockholder, owning 100 shares. The benefit is pro-rated to the length of the cruise.

Here is a discussion of this benefit from the Seabourn Cruise Critic forum.
http://boards.cruisecritic.com/showthread.php?t=1218034&highlight=carnival+stock