You don't HAVE a current clock =) That's what the external oscillator setting is for, so that it can be fed a clock from outside, not a crystal, not a resonator, a logic level pulsed input. You feed it a high/low alternating voltage (read the PDF to determine what the logic levels are for the xtal1 pin is) I think xtal 2 is the output from the internal amplifier circuitry which may not used in external oscillator mode, but is definitely not required.
I just ran across this blurb via searching, that the Dragon can't set it's ISP value until it can sense the target, it can't sense the target till the target has a clock. So just feed it ANYTHING for a brief period of time to get it to run through a few cycles =) As long as you meet the voltage level requirements of the XTAL line you can feed it a clock from nearly any source like a piezo buzzer or whatever, anything that causes the voltage on that line to toggle a logic level change for the number of cycles required to program the fuses, which isn't much.
Again, I've heard of people using rectified sound card output just to jump start AVRs back into a local oscillator mode for real reprogramming. You're not the first person to have done this by far =)