What you would need is a diode between the capacitor bank and the +5V supply rail in order to charge them up. But the diode dis-allows the 5V to remain powered up from the caps on power-off.

Click to expand...

I did exactly that ! I used a diode and stole some power from the 5V rail to charge the cap up. I could then leave the Mac off for up to 5 minutes and still be able to turn it on again without a double-flick (and the clock kept the correct time as well).