I just though, once the flash utility is running it shouldn't actually need the bios, in fact it can't need the bios because it reprograms it. So if you remove the chip from the PC while the bios flash utility has already loaded nothing bad should happen (test this first carefully) if that doesn't work then all bets are off.
It seems a little odd that they have the same bios but one is 4mbit and the other is 8, are you sure they are compatible? Also it shouldn't matter as long as the flash program doesn't try to read or write to a space that doesn't exist.