I've been looking for the same thing. I was thinking of using my quantum adapters at the flash end with a 9v transformer as power source (with appropriate jacks in between). But I don't know that a common transformer of the appropriate voltage provides enough amperage. Though I'm expect it would not be too much a task to build one.
But I've decided to do something like what's shown here (scroll toward the bottom of the page): http://www.aljacobs.com/cables-for-f.../metz-45s.html
One thing to be cautious about is the contacts between the flash and the Metz battery holder. There are 2 different "plus" contacts and a single "minus". The 2 different "plus" contacts are different in the AA alkaline holder (9v) than the nicad (7.2v) holder. While it's not explicitly stated, I'm pretty sure his approach assumes use of the Metz Nicad battery holder.
But I might use a battery holder and individual NiMH cells. The reasoning is that if an individual cell fails it can be easily replaced. The disadvantage is that you lose the more reliable soldered contact between the cells.
The contacts on my Quantum adapter match the contacts on the AA alkaline holder; which is consistent with the output voltage on the Quantum Battery 2. So I think I would want to use 8 NiMH cells for 9.6v.
Another approach would be to buy a dead or dying Quantum Battery 2 and replace the internal 8v battery yourself.