I would think an even bigger dilemma would be how to keep the frosting from getting smushed when the package it tipped over. How have you solved that problem?
I solved the crushing problem a long time ago. Whenever I get a take-out pizza, I save the little plastic thingies they use to keep the lid of the box from smashing the pizza when you stack them 10 high in the delivery vehicle.
I would mail them unfrosted with a container of frosting, a container of chopped walnuts, a plastic knife and a set of detailed instructions on how to frost them. If the person you are sending them to does not have a sense of humor they do not deserve cupcakes!
Thanks you guys for the great advice. I will try the dry ice. And the pizza container tops are a great idea too. Even considered the sending the frosting separately!
If anyone is interested, apparently there is a website called sugarcraft.com that actually sells bakery shipping items...