Now, I don't know if this would apply; probably not, but maybe something along the lines can be accomplished in a roundabout way, so here goes. I've been involved in, or participated in, cruises that were done as fundraisers for non-profit groups, such as church groups, charitable groups, etc. The entire ship wasn't booked, but a certain portion of a particular cruise would be allocated for the organization's participating passengers. When this was done, the cruise lines (everything from Princess to Celebrity to others) was very receptive. Apparently, many of the lines do this. The cost of the cruise was very inexpensive, much lower than what the other passengers paid, and a percentage went to the non-profit group sponsoring it (it was, after all, a fund-raiser). There were many perks, such as having some public rooms, or sections of them, reserved for the participants at certain times for various activities. The main organizers received their cruise for free (or, in one case, I and a friend who coordinated a fund-raiser cruise were given the option of getting the lowest grade stateroom for free, i.e., a free cruise, or pay the lowest fare stateroom and get upgraded to the one of the highest - we did that on that particular cruise and got a suite with separate bedroom, living room, dining room and marble-lined bathroom with its own jacuzzi...wow!). There were some stipulations, the main one being that there had to be a minimum number of people participating and this flucuated with the cruise lines; one required a minimum of thirty, another required more than a hundred. The thing is with that, the "kick-back" of money going to the non-profit only started with the passengers over that number. If thirty were required and only thirty sailed, the non-profit got zilch. If ninety went with a thirty minimum, then a chunk of money from the sixty-more passengers went back to the group.
I doubt if that would work with a DS cruise (saying it was to raise funds for homeless vampires probably wouldn't cut it), but maybe a cruise line would still offer a discount, such as when a hotel has a conference rate, maybe not as much if it were a fundraiser. Who knows? It would be worth looking into.
Gerard