It's pretty rare around these boards to find someone who wants to
gain weight prior to a cruise, so I think you may be hard pressed to find a support group for that.
My ideas, for what they're worth:
1) when making a sandwich don't use bread, use Poptarts.
2) take steroids or visit your local health and nutrition store and purchase some Weight Gain 5000 formula
3) have at least one alcoholic drink per day (lots of empty calories and they taste so good)
4) drink Ensure or Boost (calories in a can, baby! My brother used to drink those like crazy when he was going through chemo to try to keep his weight up)
5) never pass up a second helping of dessert