FREE DECKS. That's the last bullet in the gun, and that's what I just fired off. I added a free deck to the 6-deck package and the one that comes with a press sheet and THREE free decks to the brick level purchase.
In the end, I felt like I had to do everything possible, and while I've spent a lot of time and effort in getting the word out, I needed to do something to encourage backers to move up to a higher level. And while this will give me fewer decks to sell after the campaign and I'll soak a tiny amount of extra shipping, that's WAY better than having NO decks to sell after the campaign (and none to ship).
Initial response seems good, so hopefully I'll make the final $350 or so in the next 6 hours. And if I do, those backers are going to (rightly) get an awesome deal.