I've decided to bite the bullet and build a prototype ZIFduino board. I used the through-hole version the folks at
http://www.freeduino.org/freeduino_open_designs.html released as a template. After quite a bit of tweaking to get the monstrous ZIF socket in there, it ended up being about 25% wider. The board and parts are on order, and I should be able to assemble it in a couple weeks. In the meantime, if you want to check it out and critique (please do, this is my first real project in Eagle) the .brd and .sch files can be downloaded at
http://bitgood.org/blogfiles/ZIFduino.zip. If this works out and there's enough interest I'll make a bunch of boards and sell them at cost.
Since the vast majority of the work was done by others, I left all documentation intact and just added my name to the list. If your name is on there and you don't want it to be, let me know and it'll be removed right away.