Do generic ZIF-to-DIP adapters exist? Just plop one of those in there instead of a full-blown shield. I only saw some ridiculously expensive adapter assemblies in Digikey, but they were for ZIF-to-header or ZIF-to-PLCC.
If not, seems like a ZIF Shield might be a useful thing, but rather than draw signals from the Arduino headers, draw it directly from the DIP socket in which the ATmega168 sits.
When I think of "shield" I think of being tied to the four header rows at least for support, and the risk here is whether the DIP socket is in the same spot on each Arduino DIP revision.