USB 3.0 power levels on USB 2.0 device
The answer to a related question suggests this will not be possible. 

When operating at USB 2 (or below) the unit of power is 2mA. At USB 3.0 the unit is 8mA, allowing a higher maximum power. 

Therefore unless you can negotiate as a USB 3.0 device you will be limited to the same ~500mA maximum (an unsigned 8 bit integer multiplied by 2mA).