Hmmm... No go...
If I change the avrdude command's baud rate, then it can't communicate with the ArduinoISP sketch as that runs at 19200. If I change the ArduinoISP sketch to match, then it is exactly the same as before.
However, you might be on to something anyway. I will look at slowing down the ArduinoISP's communication with the chip if it's possible.
It's already running at Fosc/128, so that's the slowest it will go. Hmmm... tricky...
Is it possible to switch oscillators on the fly on an Atmel chip? If I could switch my running Arduino to a lower speed it might compensate. I don't want to brick this good chip by playing with fuses though.