iPad 4 not charging solution with usb 3.0 dual ports Y adapter
A few years late, but something like this will help.

SinLoon-Enhancer Y splitter Hub Adapter Cable-Female-Charge-Extension

It's a Dual Male USB Cable, one of the male connectors are for power, the other for power + data.  It should give you a full 1AH with the power connectors from both USB ports, assuming your hub can output more than 500mah total.