I like JoAnn's suggestion. I was thinking of putting those gold or foil return address lables. Not quite that small, but I bet it would be easier to have large lables made than the boxes.
I know a company that does letterhead and presentation folders, I wonder if they might be able to do cake boxes.
Another thought--
To make labels of a larger size or different shape, office supple stores sell 8.5 x 11.5" labels. It is in the shape of a sheet of paper, but the back peels off the whole thing and you have a label. I have seen them in clear or white!
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