Port redirection

Hi, How to I achieve a port redirect within the ReadyNAS unit?
Before my broadband router upgrade, I port forwarded an external port to port 22 on the ReadyNAS for remote SSH access. This worked well. However the new router provided by the broadband supplier has blocked the use of port forwarding an external port to internal port 22. So I thought i could perform a port redirect on the ReadyNAS unit.
For example, I was thinking if I port forward something like port 60000 external to 60000 internal on the router. Then on the ReadyNAS redirect port 60000 to 22. 

I see port redirection can be performed on linux using iptables with a command like this

# iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 22 -j REDIRECT --to-port 60000

Now ReadyNAS doesn't use iptables, as far as i can tell.
So I'm asking does any one know if this can be done?