Didn't user westfw come up with a bootloader 'fix' for this problem where it would report back to AVRDUDE the signature of a 328p chip even though it was installed into a 328 non p chip. Simply lying to AVRDUDE seemed to be the simplest method. I guess the trick is how to get such a 'modified' bootloader installed into a 328 non p chip in the first place, chick and egg problem? Anyway maybe contacting westfw would give you a direct path to success as I'm pretty sure he dealt with this issue in the past.
Lefty