herman428, this would be an interesting hack but all the circuitry in the iPod requires firewire for the charging, so you can not modify that. I would suggest something like a USB charger followed by a buck converter and terminate this with a firewire connection. Not really that cumbersome and should be doable. Hope this helps, good luck.
== Update ==
The "hack" on instructable is a bit different.It was developed to charge the iPod with just any generic charger The USB output will remain around 4.6V- to - 5.2 V. Firewire is at 12V, you you will have to have some sort of DC-DC step up converter.