So you're really talking an adapter like this
http://www.logicalsys.com/painfo-vpasp-vb.asp?adapter=pa-qld6sm18-32f-88
but with a couple of pins left off to go from 32 to 28.
And narrower, maybe using the pinless package, the 32M1-A, the 328-MU and the 328P-MU, both 5mm wide, while the socket pins are ~8.2mm wide
(I don't see what the difference is between 328 & 328P in the datasheet, must be something subtle I am missing).