Spray it on another piece of (preferably thick) paper, a simply a dry sponge. then rub the two together. That’s one thought.
you could as well find another piece of paper (colored construction paper could work) and spray that. Then attach it to the other paper to serve as a border.
and, I you have any blank shiny photo paper, you could do the same or rewrite the letter on that. That way it wouldn’t smear or wrinkle, and you could spray it on the back.
Hope I help! 
