Here are similar discussions, http://www.microchip.com/forums/m404231.aspx http://www.microchip.com/forums/m375994.aspx
IMHO, the effort to implement swapped configurations is unrewarded.
In most cases, single config of 500 mA will do.
The reasons are,
1) The current draw is limited to 100mA, just when your device is connected to a bus-powered hub.
2) Many hubs on the market always report its status in self-powered, even when it is actually in bus-powered.
500 mA config is not enumerated when the bus-powered hub reports its status correctly.
OS puts a warning dialog for insufficient power supply.
Therefore, you should have a warning on the manual, "When you see power supply warning, connect this device directly to the PC USB port, or over a self-powered hub".
Rather, you had better to have a VBUS voltage monitor, and a power-down circuit on your device.