You mean something like this
http://www.diatec.co.jp/shop/det.php?prod_c=138
I've been using that cable for a while now to charge my C3000's battery while on the move. I've got a nice small USB hub with a not too bulky 5V DC adapter, so basically I have the power-to-go cable connected between one of the USB connectors of the hub and the Zaurus, and I use my USB mini-A to USB adapter, and a USB to mini-B cable to connect the USB hub to the Zaurus through the USB host plug. (OMG, how confusing it sounds when I try to re-read this sentence... See the attached picture, it'll be easier to understand! It shows my Zaurus connected to the USB hub by both USB-host cable and power cable, and a bluetooth USB dongle and USB mouse connected to the hub. Works like a charm! [ Invalid Attachment ] )
All in all, my Zaurus can recharge if I don't need any particular power from the USB hub for another USB device, and if so I just disconnect the power-to-go cable and the AC adapter then powers the USB device.
I'm not sure if sharing the same USB port to plug a cable that would go to the Zaurus USB host plug AND to the Zaurus DC plug would work (maybe there are electrical implications to doing that, like the Zaurus DC requiring too much power and conflicting with the normal USB link), but OTOH I don't see any reason why it wouldn't work. It's close to what I'm doing right now, except that the USB cable is plugged to a different port on the HUB than the DC cable...