If the drive is shipping with the Y cable, it pretty much means that it
does not meet the USB spec limit of 500 mA port power, it requires
more. Most all devices with USB ports will only deliver 500 mA per
port, since that is the spec.
If you cannot spare a port for the extra power, perhaps you may
consider on of the USB->cell phone chargers. Most of these
will deliver on the order of 1 amp current. You could somehow
plug the one connector of the Y to that and the other to the