There is a guy marketing ready made adapter cables, but I don't like his design much.

I got my DA booting with +5VSB going into the +27V line, but obviously that means no ADC or powered Firewire devices. I've considered adding one or two of these cheap adjustable DC-DC voltage boosters inline to make up the +27V, or a Powerbook power supply (+24V) but I've moved onto a QS since then and let that project lapse.