Ok I'm actually really proud of this idea. In this Snail Mail My Email request, the writer only asked for "mail art," without specifying anything in particular. In her letter she made a cute little Christmas wish-list, which included among other things a blue typewriter and another cat (or three or five).
So I painted up a blue typewriter, and cut a small slot in the top, about where the paper would go on a real typewriter. Then I wrote the letter on segments of paint-chip cards, and inserted them into the typewriter so that they would slide upwards to be read (like paper in a real typewriter). I'm really pleased with the results, and think you could use this in loads of ways. Like, typewriting the message itself and turning the idea into party invitations?
For the mail-art part of the letter, I decided to go with "crazy-but-adorable cat-lady," for a bit of fun.