I don't know why nobody has mentioned this (yet), but there IS a way past Oak/Coffee Guy (A.K.A. "Progress Prevention Glitch" as I've seen it called). Simply perform the bad save after delivering the Parcel. Sure, you lose Pikachu (forever AFAIK), but you gain memory editing power.
You can later remove the corrupt Pokemon team by catching a Pokemon (not sure if Pikachu counts (yet)), and depositing anything invalid into the PC boxes and Releasing them. Or keep them, I don't care.
Not sure the side effects of switching any leftover invalids around in the party are, but I caught a legitimate Ditto at some point and its OT ID stopped matching my Trainer ID. (Possibly because I fiddle with the items, not sure).
Notes of interest are the Surfboard item, giving you access to Cinnabar Island very early (and a chance to catch Ditto lol).