(It doesn't have to be a surprise, for obvious reasons.)
Here's my idea.

Anyone who wants to get on board just has to pony up postage to send the card to the next person in line.
I'll manage the addresses so there's no privacy concern (although one other person will have to get your mailing address, to send it along to you).
Thoughts? Feedback? If you want in, PM me your mailing address. I'll work out an itinerary for the cards.
If someone crafty/artistic wants to volunteer to actually make the cards, that would be extra-special: let me know!