If you have two Intel based ReadyNAS units, the ReadyNAS Replicate service can be used. Pretty sure Chris had an NV+ though, so thats out.

I was also going to suggest Egnyte, but it looks like their options are a bit pricy for what you want. Still aimed mostly at document cloud activity, not photos. I beta tested this alongside my ReadyNAS Ultra, and it was pretty clever. Any files in a share could then be accessed in the cloud, or at another remote location over the LAN to a local NAS.

Ultimately the easiest solution will probably be root access to the NAS and scripting a little rsync solution up. The only downside I can see to this idea is rsync is really slow on the NV+ due to the sparc CPU, and worse when SSH overhead is added. Possibly slower then the 10mbit upstream speed. You will probably want to do the initial sync with both units on the same LAN, and NFS mount the second NAS from the first. Then use normal copy tools.

*edit* Looks like Andy is saying you might be able to do a LAN VPN to VPN easily. If so, the built in backup via the web interface should work, I'd recommend using remote NFS server if you choose this route, and have the remote NV+ have NFS enabled.

Also, 10mbit upstream service would be nice. Currently on the highest plan from Cox, and it's still only 5mbit upload.