Yep! That worked. I set the clock source (D9) from the Arduino to 128KHz and connected it to XTAL2. After that, I went into AVR Studio and set the rate to 4.209KHz (or something very close) and the connection was very unstable. Though, I was able to set the fuses back to factory state after trying to write them a few times. Now it's working without the external clock source!
I'm glad you got it working. 4.2KHz was a little too high, that might be why it was unstable. Anyway, you should be back to using the internal oscillator divided by 8 now.
You might want to try a fuse setting that leaves CLKOUT enabled, such as 0xAE or 0xBF instead of 0xEE or 0xFF. That way you can easily check with your logic analyser that the resonator is oscillating.