If the dress can be washed or dry cleaned, maybe the easiest way would be to use spray baste to attach the design and then sew it down by hand. Some spray baste goes away after a few days. Sulky is one like that, but although I was told it would hold only for 5 days, it hung around longer than that. It probably depends on how much you use and maybe factors related to climate conditions. Sulky and 505 are re-positionable for a time, so there's little risk, unlike bonding web, which would have to be reheated and would leave residue. I think I would spray the back of the applique rather than the dress itself, and if part of the design is going to extend into the neckline or whatever, you can mask that off with paper before spraying. I'd love to see a picture of the finished dress, if you get the chance to post it.