That sounds like a good idea, get a tiny usb hub and add external power (even some without the jack have the pads on the PCB once you open the case).
I would power from AA's or AAA's instead of a 9v battery. A 9v battery has a very low mAH rating which makes is a poor power choice. Most USB hubs are 5v internally anyway so 4 AA/AAA's giving 6v and a lod drop out regulator would be ideal as there would be less waste in the regulator as well.