This works if you only have one destination in mind, but I have 4 or so boxes on the LAN that all run sshd--the fancy simulation box, two hacked Linksys NSLU2 NAS devices, and a desktop machine. That means that I either have to put all but one on nonstandard ports, which makes life complicated, or else have a router that supports port translation so that they can talk to different ports on the WAN connection. (Or use a server as linnix suggested, and have it be an ssh proxy along with its other jobs.) The same applies to running rsync on all these boxes.
I'm well outside my comfort zone here, because network configuration can be a real time sink even for folks that are good at it.
Thanks
Phil Hobbs