Mount the disk using udev. Place the rules from this wiki into
/etc/udev/user.rules and reboot (or reconnect the USB HDD) . There are several favors of rules in the wiki (that's why I didn't list them here), choose the one that best suits your needs (e.g. you need a specific normal user to be able to unmount it).
/lib/udev/rules.d/80-udisks.rules will help you understand what's udev doing to your hard disk.
Besides the udev rules I mentioned above I think there's another approach you can take: instruct udisks (through udev) to leave your disk alone and then mount it through fstab.
This code works on my system
but is generic and includes all partitions. To be able to target your particular hdd/partition use
udevadm info --query=all -n /dev/sdX and then match on some of those particular atributes in the udev rules.
A good resource to help you in this is Writing udev rules. Unfortunately it contains some outdated info (
udevinfo was replaced by
udevadm indo). I assure you, though, it's a worthwhile read -- udev is a central piece of architecture nowadays and you can accomplish a lot by using it. It's also pretty flexible.
It's also easy to make mistakes in udev rules :). Use
udevadm test $(udevadm info -q path -n /dev/sdX) to take a 'peek' at what's udev doing.