Bet it wouldn't take much. Looks a 168 with 1/2 the memory.
http://www.atmel.com/devices/ATMEGA88.aspx?tab=documents ATmega88/168 datasheet
-
make sure there's an entry for it in avrdude.conf - possibly copy the 168 section, update the signature bytes and memory sizes
-
make a new entry in boards.txt, again copy the 168 section and tweak as needed
-
update pins_arduino.h to call out the new type in a few places
Probably put pins_arduino.h in a new variants folder in the 1.0.1 directory somewhere.