That might be quick enough, but if it isn't there is an alternative you can try.

Normally when there is no USB connection active, the usb_moded daemon removes the driver modules from kernel. When you need to have IP connection to the device, the module g_ether.ko is loaded, and when you need USB storage connection, the module g_file_storage.ko is loaded.

If you disable usb_moded and load g_file_storage.ko before connecting the USB to the device you'll have the drive emulation working immediately.