Are you sure SSH access isn't already on? With version 4 of the firmware for my NV+, it was just automatically on, and it used the web admin password as the root password. Rsync over SSH works either direction as well, with no setup or changes.

*edit* never mind, I'm getting it backwards. 3 had SSH on by default for support reasons, but someone figured out the algorithm they used to generate root passwords. So it's off by default, but is toggled on by using the Netgear provided addon. I applied that shortly after updating to 4.0.

I haven't poked at the rsync options in the WebUI, but I did find someone saying that you can enable rsync over SSH in the GUI by editing /etc/default/services, and add a "RSYNC_OVER_SSH=1" to it.