Help with square save the dates/non-machinable?

Hey all! Longtime lurker, first time poster. I spent hours creating our wedding suite and save the dates with our designer only to be told that the square shape of the save the dates is “non-machinable” so I would need to use a butterfly stamp specific to this dilemma. I hate to ruin the beautiful work we created with the butterfly. I know it’s ridiculous but all that effort to see a butterfly stamp I didn’t choose just makes me so sad.

Has anyone had experience with this and ways around it? I don’t mind paying extra for more postage, but I’m confused on how much I would need. The save the dates weigh about 1.5 oz. Thank you so much in advance!