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!